If you have bootloader v1.0012 (1.12) you are lucky and can upgrade to v5.5022.
Download the bootloader file, for exemple here
Extract the file called system to your Tomtom and reboot it. Make sure that your battery if fully charged before attempting the upgrade.
After it has again booted, you can remove the file system since its payload is now written in the bootloader eprom. Do not delete TTSYSTEM, this is the navcore.
Bootloader 1.0000 and 10010 can not be upgraded and any attempt in doing so might brick a tomtom.