This firmware version has only been released for the new Clara HD, and there appears to be no official download link yet. See geek1011's post in the Clara discussion thread for a link to kobo-update-4.8.11090.zip.
Before starting:
1. Check Settings > Device information to make sure your Kobo ereader is already running firmware version 4.8.11090 (bee5052c41). If not, then you need to upgrade before applying this patch.
2. Check that your battery is well charged.
Patching from Windows, Linux (i386/x86_64/ARM), or Mac (OS X 10.8-10.9, i386/x86_64):
1. Download and extract patch_kobo_40811090.zip (attached).
2. Download the Kobo firmware archive version 4.8.11090 for your device (See this post for links) and copy it into the 4.8.11090_source/ subdirectory that was created in step 1. (Don't unzip the firmware archive.)
3. Read and edit all the *.patch files in the 4.8.11090_source/ subdirectory in order to: choose which patches to enable (patch_enable=`yes`) or disable (patch_enable=`no`); and to change some of the replacement values to suit your device and preferences.
4. In Windows run 4.8.11090.bat (double-click); For Linux/Mac run 4.8.11090.sh (double-click, or right-click + run, or execute 4.8.11090.sh from the command line, or drag 4.8.11090.sh into Terminal, depending on your particular OS/desktop.)
5. If there were no errors, a new 4.8.11090_target/ subdirectory will be created. Copy the KoboRoot.tgz file from this subdirectory to the .kobo directory on your ereader.
6. Safely eject and unplug the device, which will then update and restart.
To return your ereader to its original unpatched state:
1. Edit all the 4.8.11090_source/*.patch files to disable all patches (i.e. set patch_enable = `no` for every patch).
2. Repeat steps 4-6 of the procedure above.
Before starting:
1. Check Settings > Device information to make sure your Kobo ereader is already running firmware version 4.8.11090 (bee5052c41). If not, then you need to upgrade before applying this patch.
2. Check that your battery is well charged.
Patching from Windows, Linux (i386/x86_64/ARM), or Mac (OS X 10.8-10.9, i386/x86_64):
1. Download and extract patch_kobo_40811090.zip (attached).
2. Download the Kobo firmware archive version 4.8.11090 for your device (See this post for links) and copy it into the 4.8.11090_source/ subdirectory that was created in step 1. (Don't unzip the firmware archive.)
3. Read and edit all the *.patch files in the 4.8.11090_source/ subdirectory in order to: choose which patches to enable (patch_enable=`yes`) or disable (patch_enable=`no`); and to change some of the replacement values to suit your device and preferences.
4. In Windows run 4.8.11090.bat (double-click); For Linux/Mac run 4.8.11090.sh (double-click, or right-click + run, or execute 4.8.11090.sh from the command line, or drag 4.8.11090.sh into Terminal, depending on your particular OS/desktop.)
5. If there were no errors, a new 4.8.11090_target/ subdirectory will be created. Copy the KoboRoot.tgz file from this subdirectory to the .kobo directory on your ereader.
6. Safely eject and unplug the device, which will then update and restart.
To return your ereader to its original unpatched state:
1. Edit all the 4.8.11090_source/*.patch files to disable all patches (i.e. set patch_enable = `no` for every patch).
2. Repeat steps 4-6 of the procedure above.