Assumptions:
1) you've tested everything locally and it works,
2) your current site is in
/OLD
folder
Then I normally would do following:
- install a new generic XOOPS website in /NEW folder
- copy /upgrade folder to /NEW folder
- copy all the required and tested modules to /NEW/modules (you don't need to install them)
- copy from the /OLD website all custom files, avatars, images etc. from individual modules and from /uploads
- in /xoops_data/data/secure.php change the Database info (location, user name, password, etc) to the old Website's database.
- in mainfile.php change the Domain URL info
- in Admin Preference, turn the current site off
- make a BACKUP of everything, especially the Database
- on the host, redirect the Domain to the /NEW directory.
- go to
http://mysite.com/upgrade and run it
- the Website should now work.
- if there any issues (missing images, not updated modules) -> fix them
- turn on the Website for your users
Once tested and working, delete the /OLD folder with all the files, but keep a backup, just in case, especially of the Database. And drop the empty database that you've installed as first with the new fresh installation, before switching to the old database.
What you're basically doing is to install new XOOPS, but then switch to the old database and use it.