Heya darling!
So, the best way to get these levels is to earn them. There are many opportunities for leveling in elsewhere, like joining institutions and completing private threads. You can also take advantage of our gringotts system to buy levels.
Additionally, it is possible to submit a special request for higher levels. You would also need to special request to be an animagus.
If there is anything you are unclear on, please let us know.