* First, I would recommend to set up a test site, with PHP 5, and copy your current site there. Also, copy the current DB to a new one, that you would be using on the test site. You can do it on your current server, but it's easier to use something like
WAMPServer on your local PC.
* Once you have it there, then make sure that all your links in mainfile.php are updated correctly and pointing to the new test site.
* Follow the instructions for full Update and copy the XOOPS 2.5.4 files as instructed (before you do it, make sure that you delete the /module/system directory)
* copy and run /upgrade (as explained in the instructions) and in the Admin update the system module (this should be the last step in your Upgrade script above)
Now the fun part begins
Several of the modules might not work, because you'll be on PHP 5.
Of the modules that I am aware of, you'll need to update several of them:
Forum 3.05 => at least 3.08, but we'll have soon 4.10, so you might wait 3-4 weeks.
Files 1.20 (I don't know it)
protector 3.04 ==> this will be updated with the XOOPS Update
articls 1.03 (don't know it)
communication 1.27 (don't know it)
F.A.Q 1.08 ==> 1.23 coming soon
relative links 0.97 (don't know it)
Tips and Tricks 1.00 (don't know it)
Shoutbox 4.05 (I think, it should run)
Polls 1.30 ==> it should work, but 1.33 coming soon
Sitemap 1.30 ==> it should work
News 1.56 ==> at least 1.66, but 1.67 coming soon
XOOPS Info 2.14 (you probably don't need it anymore)
Captcha Module 0.11 (don't know it - what do you use it for?)
SmartObject Framework 0.90
AVAMAN 0.21 (should work)
Site Statistics 0.45 (don't know it)
d3pipes 0.56
ALTSYS 0.55 ==> at least 0.71, but I think, there is a newer one from Japan
Photos 2.84(don't know it)
message manage 2.63 (don't know it)
My tabs 2.10 (should work)
Important things:
1) make sure that you read the info about Protector, and the proper position of "Trust path"
2) If you have problems with blank screens, deactivate modules in your database using phpMyAdmin (except the System module), and then add them one by one to identify those causing the problem.
Some of the modules above might be outdated, and their functionality might be found in some other newer modules, so you actually might get rid of them.
Hopefully some other people provide info about modules that I don't know.