Please wait to trim your Acacia. If you remove branches and foliage now you will run the risk of sunburning some of the remaining parts, especially the trunk.

Plus, each leaf you leave on the tree is manufacturing sugars that the tree needs to grow. Remove the leaves = starve the tree.

If you must prune, don't remove the whole branch. Instead start at the tips of the branches and work backwards removing a foot or two and being careful to cut where the shoot intersects with another one. Wait until next May to remove the lower branches completely.

A great reference for pruning is Pruning, Planting and Care by Eric Johnson (Ironwood Press). You can find it at local bookstores or on-line.