Well, you can upgrade either way; the recommended is to overwrite the language files; it ensures everything is there no matter what; HOWEVER, if you run the upgrade script with files missing it'll tell you what is new and needs to be uploaded and will modify your files for you should you hae them chmodded 666 (so if you follow it then it's a worthwhile way of preserving changes).

I am a Web Development Contractor, I do not work for UBBCentral. I have provided free User to User Support since the beginning of these support forums.
Do you need Forum Install or Upgrade Services?
Forums: A Gardeners Forum
UBB.threads: UBBWiki, UBB Styles, UBB.Sitemaps
Longtime Supporter & Resident Post-A-Holic
VNC Web Services: Code Modifications, Upgrades, Styling, Coding Services, Disaster Recovery, and more!