Patrick first as the migration from 44xx to 25xx ,so HA is not possible.
Secondly you can use WCS for backup or use manual process which is indicated below.
http://mrncciew.com/2013/01/25/backup-restore-wlc-configs/
NOTE: AP Name & Locations won't be in a WLC backup configuration,remaining will be there.
Also i have not come across any official migration document so you have to use the manual process as indicated above.
Hope this will hep :)