The Us are currently down in 18th place in the Championship table, although Cowling believes that Williams has got the side on the right track.
He told the Gazette: "We're always looking for ways to strengthen the squad, but we have to ensure that we identify and bring in players who are at least better than what we have already got.
"There are lots of things that we are doing at this club that will make it a more attractive proposition for future players.
"But we have to remember that we have a good set of pros at the club already. They're tremendous and are getting results."