Help with sleeves?

Hello! I was wondering if somebody could help me with a sleeves issue? I bought a dress a while ago, despite the fact that it wasn't available in my size. I just loved it so much! It had 3/4 length sleeves which I had shortened and the fabric removed was used to make the waist bigger.

The problem now is that the short sleeves are a little too tight (and aren't that flattering anyway) and I was thinking of making them into cap-sleeves. How easy would this be to do? Would I have to remove the whole sleeve? I dont really sew, but can be ok at it when necessary (made myself a simple dress with a circle skirt for hallowe'en - first proper attempt at sewing!).

Here's the top of the dress, please ignore the stains, it's going to the dry cleaner tomorrow. Here's me in it.

Any advice would be much appreciated. Thanks in advance.

EDIT After detaching the sleeves, cutting them shorter, adding some pleats and then pinning them back onto the dress I just couldn't get them to look right. I decided in the end to just leave them off entirely and the dress is now sleeveless.