join to domain if not already.
from localadmin account (not account being converted)
from terminal:
sudo dscl . delete /Users/USERNAME
logout and connect to network and login with users domain account and everything should be fine.
Note: if you do not see "other user" on login screen or "network users can loign" in users and groups in sys prefs the system needs to be removed and rejoined to domain.
if username is different or if you run into any permission issues try the following:
Change the name of the local home folder to match the directory short name. The command is posted below (substitute USERNAME for the original short name, and DIRUSERNAME for the directory short name).
sudo mv /Users/USERNAME /Users/DIRUSERNAME
Log out to test the new account.
At the login screen, select 'Other' or simply type the user's network credentials.
Clean Up Permissions
On the first login it is entirely normal to receive permissions errors. These can be corrected using two Terminal commands. Substitute USERNAME for the directory short name, and DOMAIN for the sub-domain of your directory server. IMPORTANT: You will want to run these two commands from an account other than the newly converted network account.
sudo chown -R USERNAME:"DOMAIN\domain users" /Users/USERNAME
sudo chmod -R 755 /Users/USERNAME
Additionally, there are some applications which hard-code the path to support files in their preference plists. These applications will break if the username was changed. Ensure that all applications launch appropriately and modify the plists using a text editor to correct the path, or delete the plist, re-launch the application and re-configure the settings.
source:
http://robotcloud.screenstepslive.com/s/2459/m/5322/l/112415-convert-local-accounts-to-network-mobile-accounts