TMP - Age up Anakin to about 17/18.
AOTC - Give Obi-Wan another pupil, who is also tempted towards the dark side.
ROTS - Make it look like Anakin and the other pupil die about midway through the movie, with proto-Vader (mask, but no life support suit) taking his place.

ANH - Fix the Death Star plans graphics.
ESB - Include a line from Lando about Han endangering the people of Bespin (thanks, RougeLeader)
ROTJ - Replace the Second Death Star with a skyhook above a volcanic planet (basically Mustafar).

R1 - No puns from Vader.
Solo - No imperial officer giving Han his surname.

TFA - No Starkiller Base.
TLJ - No green milk scene.