Sounds like you bought a black cow - perhaps with Angus heritage.
IF she is the product of two registered Angus cattle, the breeder/original owner might be able to go back and register her - I've not read the AAA's regulations - but if allowed, it'll likely be costly, and they'll probably require parentage verification to the alleged dam and sire via blood-typing/DNA analysis.
If you're wanting a registered Angus calf, you're probably just gonna have to buy registered stock; may be the cheapest and easiest way.
AAA does not have a 'grading up' program.
Some other breeds will allow you to register % calves out of unregistered grade cattle.
For example, I started out breeding up toward purebred status, with Simmental sires back in the late 80s, on unregistered commercial Angus(and a few Holstein) cows. Never got to purebred status with any of 'em before life got in the way - but wasn't far off from it with some of 'em.
Red Angus Assn. has something of a 'grade up' program, but as I read it, you can never reach Category IA unless you start with registered Red Angus stock.