Ya, there are bolts in the back the hold the axle on which will need to be loosened so that you can use the chain adjuster to pull the axle backwards. Make sure that you tighten everything down well when you are done. There should be a little play in the chain. You may need a new chain and sprockets though. If the teeth are worn on one side so that they all are pointing more in a circle dirction then straight out, you need to replace them. If you look on the stearing stem tube under the forks there should be a sticker with your trikes year, if not find the number on the frame or engine and compare just so you know. The model numbers are posted here if you search for them.
Anyone know of a new project machine for me around Wisconsin?