XOOPS 2.5.5 is not yet released, so please don't use it on a production sites.
Reg. update itself from 2.4.4 - there shouldn't be anything special, besides the regular:
- make a backup, create a test site with your current data, and test there before you upgrade the "production" site
- if you have currently PHP4, make sure that you have updated to PHP 5, as this is the requirement for XOOPS 2.5.4
- check if there are newer update module versions, so you can use them
From Ohio, USA