First, figure out how much you need to cut off and measure it with your little hem ruler. I measured up 1-1/2", which means I was cutting off a total of 3". Be sure to double whatever your measurement is.
Then pin the heck out of it.
Next, sew all the way around the bottom. I used my zipper foot so that I could get as close to the hem as possible. Be sure to remove your pins as you go.
Stop to take a picture of a cute kid.
I finished mine off by serging off the extra and making a nice finished edge. If you don't have a serger, you could cut it off with scissors and use a zig-zag or overlocking stitch to finish the edge.
Here's the final project. You really can't tell they're hemmed unless you look really, really close.