You can install Python2.6 as user-executable software in your home directory which will work alongside with the existing Python2.4 (used by the system). Do not try installing Python2.6 on the F5 appliance globally! It will probably screw up the system as there are no guarantees the scripts in use by the BigIP software will work after a global Python upgrade to 2.6.
As far as the installation procedure goes, look for Linux RHEL4 .rpm packages.
Following a successful installation, you also need to modify the bigsuds config to point to Python2.6, or else it will complain about the outdated Python2.4 version (system default).
In general, I only recommend you try this if you are feeling confident in Linux RHEL environment. This is not something you should try otherwise.