Depends actually. Does 2.x mean 2.0, 2.1 or 2.2? There is a difference.
If it's 2.1 or 2.2, then:
In the old blog click Manage > Export > and save the file
In the new blog click Manage > Import > and upload the file
If you have 2.0, you're going to have issues with the transfer. Best bet would be to upgrade to 2.2 and then do the export. There was a plugin for 2.0 but the format's been changed during the upgrades.
Gotta admit that this has been covered many times over here in the forums. May want to try to get comfortable with searching.
Hope this helps,
-drmike