I don't know for sure if TL5 is the same as the HD3 for this (I'm guessing it is)... this is how I updated my HD3 (support told another user, teriyake, to use this procedure and he/she shared it in another thread).
- Unpack the zip file in the main PocketBook folder.
- Turn off the PocketBook (completely, hold down off/on key for a few seconds)
- Push and hold the Forward and Backyard Page turn buttons while simultaneously pushing the Power Button. Hold the Page turn buttons until the screen says "Firmware Updating."
- Wait. I think I had to wait for five minutes and about two reloads before it was done.
I hope this helps. Good luck.