The first way of making a minifugure taller is by using this "belt". To make it just cut the midle stripe of the piece shown.
Put the piece on tom of the fugures legs and there you have it, now it is taller. (You should put some tape because the uper part of the body will fall.)
The second way is by using these 1x1 square pieces.
Just put them on the minifigure's feet and your figures has new shoes.
The minifigure will be more balanced in size if you use both ways.