For clix:

The use of the official iriver MTP firmware updater is recommended for updating clix. A simple guide can be found here. If you have trouble getting the updater to 'see' your clix, you can try a manual update, here is a guide by Ted Yo!:

Quote:

Originally Posted by Ted Yo! Grab the correct firmware from: iRiver Firmware Updates If you have a 2G clix, the correct versions are labeled "Clix 2G", the 4G firmware is "Clix 4G". The last three letters are the language (English is ENG). After downloading the firmware, extract the HEX file from the zip. Plug in your device. Open My Computer Open the Clix WMP10: Open the data folder WMP11: Open the root storage Copy the hex file that you unzipped into this folder. Unplug your device. After the firmware update has completed, format your device. Transfer your content back to it.

The latest firmware for 2GB clix is v2.01; the latest firmware for 4GB clix is v2.00.
There is no v2.2 firmware for clix. It is only a typo on iriver America site.
[UPDATE] You can also find firmware v2.12 for clix1, but be mind of 2 things: 1) It adds Play-From-Device function to your clix, allowing any other PFD supported player (such as some car stereo) to playback DRM'ed files from clix. 2) The updating process can only be done manually and it is non-reversible.

Firmware 2.12 is basically a firmware 2.00/2.01 with PFD support. There is no need to update unless you want to use PFD function. If you do want to update, there are two firmware for each model: clix 2GB has 'CLIX 2G' and 'CLIX PFD' without '3855' on identifier; clix 4G has 'CLIX 4G' and 'CLIX PFD' with '3855' in identifier. Important: Get the larger of the two files that fit your clix model, you should find two .HEX files in it and you need to drag and drop BOTH into your clix root directory.

For clix2: (as of Dec 21st, 2007)

If you are using MTP mode, firmware updater is recommended. If you are using UMS (MSC) mode, iriver plus 3 can be used to automatically update you clix2.

If you want to update firmware manually in either MTP or UMS mode, follow the above procedure for MTP clix (MSC mode just copy the HEX file to root folder) and observe the following changes:

Currently, only Rhapsody compatible clix2 use the Rhapsody enable firmware (v1.16). You can switch your 2GB/4GB/8GB clix2 to Rhapsody compatible by manually update your clix2 with this firmware. Users of 8GB clix2 who want to use Rhapsody service are recommended to update to the latest Rhapsody firmware v1.16 in order to utilize the whole memory capacity.

For clix2 international model (English):

For those of you who doesn't want to use Rhapsody service, please download the firmware labeled as 'CLIX', version '1.16', Identifier with '0x4102_0x1126_N_ENG' and simply extract the .HEX file to the root folder of your clix2.

For those of you who does want to use Rhapsody service, please download the firmware labeled as 'CLIX', version '1.16', Identifier '0x4102_0x1126_N_BAS' and simply extract the .HEX file to the root folder of your clix2.

For clix2 Korean model:

For those of you who doesn't want to use Rhapsody service, please download the firmware labeled as 'CLIX', version '1.16', Identifier with 'CLIX_ENG_UM_OK' and simply extract the .HEX file to the root folder of your clix2.

For those of you who does want to use Rhapsody service, please download the firmware labeled as 'CLIX', version '1.16', Identifier 'CLIX_BAS_UM_OK' and simply extract the .HEX file to the root folder of your clix2.

Unplug your device once you copy the file into your clix2. Reset it if it doesn't reset itself automatically. Once reseted, it will 'freeze' at the startup screen indicating the player is updating its firmware. Do not press any button until the 'freezing' is over (or risk 'bricking' your clix2).

*Please notice, the version mentioned above are only accurate at the date of this post being updated. Newer version might be released before this post being updated, so please refer to the Identifier to help you on finding the correct firmware.

Important Reminder:

1. Manual update should only be your last resolve.
2. Always backup data (copy and paste) before updating.
3. Always be sure to fully charge your player before updating.
4. The updating process can be time consuming. If the player resets itself and seems to stop at the startup screen, please be patient and give it 15~30 minutes before hitting the reset button. If you reseted your device before completing the update, it will automatically restart the process (and stop at the startup screen again). This means you need to give it more time to complete the process. Do remember: There is a chance you can brick your clix2 if you reseted your clix2 at a 'wrong time'.
5. Always remember to format your player once the updating is completed. Reason has been given in another FAQ.
   

For those who are interesting in older clix2's firmware version, there is a firmware archive in the clix2 firmware discussion forum.

[UPDATE] All 8GB clix2 should update to v1.14 (or above) ASAP to resolve the limited memory issue in MTP mode.