I just did this..its easy.
1) make a backup of old data store in Sql
2)on new sql, make a new database with same name as old and restore the backup from old, overwriting everything.
3)repoint your ODBC to new sql server.
4) at command prompt type in dsmaint recreatelhc
5)login to the Management console to make sure you can reach the datastore. If successful...reboot. If fails..repeat step 3,4,5. Then reboot server.
You must do this on all servers in farm.