more than likely you will have to take some links out.
I went from a 44 tooth to a 41 tooth and i had to remove links (i was not running a tensioner at all at this time).
just 3 teeth smaller on the rear sprocket and i had to remove 2 links. i have since made and installed a tensioner with a spring for up & down movement, and my chain is now perfect.
you're going from a 44 to a 38, which is a whole heck of a lot smaller sprocket.
Unless your tensioner has a whole bunch of adjustment left, you will more than likely have to remove links from the chain.