Fist of all, before you update, make a backup of the file default.mddbs
directory (it is your savegame).
Update to which version?
I guess you had the 2011-02-12 version before.
Changes when you switch version to:
- 2011-05-04s: water will flow, wood becomes chest
- 2012-02-02 (latest nightly build): new map generator, new textures
You can import your map there, but if you explore new parts of the map, the new generator is being used and generates ugly transitions to the old sections.
I suggest just to try it out. Just in case, you have still your backup.