Just upgraded Movable Type from version 2.21 to 2.51. Process involved downloading Movable Type 2.51 Upgrade Version, uploading files to my server's mt directory (replacing old files/directories), setting permissions of *.cgi files to 755 (chmod 755 *.cgi), deleting mt-upgrade*.cgi files (rm mt-upgrade*.cgi), then rebuilding site. Important: For extlib directory, transfer over contents of that directory — don't just replace entire directory. Full upgrade instructions are here. Not sure what new features I can take advantage of yet... Local blog search would be nice. Will see...

Oh, before I upgraded, I exported all my entries to a text file (Utilities => Import/Export button) and I FTP'd over the db directory on my server to my local disk as backup.