[Ashur]

depends on your priorities
if you want 0 loss of data then probably very tough
if you're wiling to sacrifice few things then it gets easier and if you just care about the users then it's very feasible

basically you need to modify your current tracker's 'users' table structure to of that 5.4.1 but also type of data input you might run into a brick of having all type of info of users to be transferred over but then here are major information need to be transferred
1. username
2. email address
here is something probably good idea to transfer ID number, join date & amount uploaded/downloaded
other than that the other info is probably not useful or important

how to do all this fun stuff? well phpmyadmin is the way so learn how to use it
also do tons of backup

it's 2:00am and not sure what the heck I typed but now going to sleep

Good Luck