Measure the width between the existing fence posts. Measure from the top center of each post, since you’ll be adding lattice and attaching it to an extension of the existing posts.
Cut lattice sheets to the width between the posts using a circular saw or table saw. Ideally, your posts will be set 8 feet apart, which corresponds to the width of a standard sheet of lattice, so you won’t have to make any cuts to the width. Also determine how much added height you want on the fence and cut your lattice to the appropriate height. Two feet of extension usually works well, so you can cut a 4-by-8-foot piece of lattice in two and use both sides as extension pieces.
Cut 4-by-4-inch post into 2-foot pieces using a circular or table saw, for your fence extension posts. Most fence posts are made with 4-by-4-inch posts, but measure your fence posts and use posts of the same dimensions.
Use a drill to secure a metal tie plate to the bottom of each fence extension post, leaving half of the metal tie plate hanging from the bottom of each post. Then secure the hanging portion of the tie plate to the existing fence posts. Your screws should be about 2 inches long.
Place your cut lattice sheets against the fence extension posts and secure them to the posts by drilling screws through the lattice and into the extension posts.