Help turning a long vest into a short vest

Hi All, I am very new at sewing and this will be my first attempt at clothes (if you don't count the pair of sleep pants that took a bad turn around the crotch)  . Anyhow, with that behind me I have a long polyester vest (goes past this hips) that I desperately want to wear but it really needs to be a bit shorter. I don't really know how to begin past cutting in with a seam allowance. What type of stitch would I use for this? What steps should I take? Also, how do you add a pictures to your posts? When I click on the Image button it does this ( )? Thanks so much for your help.