The Swans have been involved in a relegation fight this season and Williams has deemed the performances unacceptable.
However, following a recent run of results, the Swans have pulled away from the relegation zone but the centre-back is aware it has been a subpar campaign at the Liberty Stadium.
"We have got it wrong for whatever reason, and it's unacceptable for a club like Swansea to have a season like this with the players we have got," said Williams.
"We need to do better as a club and there is a lot of talking to be done in the summer.
"There are many reasons why we haven't done well and the squad has a lot of reflecting to do.
"There's a lot been going on and we need to have that review - all of us individually, as a team and the chairman - to have a much better and smoother season next time."