First, confirm that you made the sleeve big enough for your arm
![Grin ;D](https://www.kumoricon.org/forums/Smileys/default/grin.gif)
If not, you WILL have to cut a new sleeve no matter what, so be sure to make it big enough to fit this time.
If the sleeve does fit you, you have a few options:
(1) cut a new sleeve that is wide enough at the top to fill the arm hole, and then tapers down to the original sleeve size by the elbow area.
(2) cut a wedge of fabric - known as a gusset - to fill in the extra (this is more or less like cutting a second sleeve piece but it would taper down to nothing in about 6"
(3) put a running stitch in the armhole and gather it until you've shrunk the hole down to the same size as the top of the sleeve.