If you use Debian (or a derivitive there of (Ubuntu, Mepis, etc)), then simply installing the latest .deb package file will do the update job.
dpkg -i The Debian repositories have mt-daapd in them IIRC, but there is only the stable version available (mixed with a very old nightlie iirc).
Incidently I’ve got mt-daapd running perfectly (svn-1586) on Debian ‘Unstable’ (Debian ‘Lenny/Sid’?).
The ‘sarge’ package will no work on Debian ‘Unstable/Sid’ or iirc Testing/Lenny’.
Use The Ubuntu Dapper package instead.
(will be adding this to the wiki at some point I think).
Kelly