There should be a tag on the evaporator giving the typr and charge weight. That's going to be up under the dash. There may also be an ID plate around the radiator where you normally see stickers and such. I'm speaking generally because I'm a marine AC guy, not automotive.
Also, at some point, the car makers started using different size service ports, 1/4" and 3/8" instead of having them both 1/4" ports. That was done because of the many reports of unknowing shade tree mechanic trying to recharge their systems, hooking the low press hose to the high side and having the 1 lb cans blow p in their faces.
As stated above, if you are not familiar with auto ACs and it sounds like you are not, then letting a pro do it is definitely the way to go.