2
make backup your files and the Database.
Load archive from SF.net:
http://sourceforge.net/projects/xoops/files/XOOPS%20Core%20%28stable%20releases%29/XOOPS%202.4.1/xoops-2.4.1.zip/download
unzip the archive
remove the mainfile.php (from this arcive! not from web!!!)
upload all files from /htdocs in your web
upload folder /upgrade in your XOOPS_ROOT
login in your website
set Theme und Templates to default
enable debug
start the upgrade with
http://< yourSite >/upgrade
when all points green, ready this upgrade