He departs after scoring 110 goals in 172 appearances and spent last season on loan at Wigan Athletic and Bradford City.
Signed from Cambridge United on a free transfer under manager Phil Parkinson, he scored on his league debut and quickly became prolific.
In his first season he scored 32 goals in 44 games, including an FA Trophy semi-final stoppage-time winner against Stockport County, and was named Player of the Season.
The following campaign, he scored 47 goals in 53 matches, helping win the National League title with a decisive double against Boreham Wood, and finished as FA Cup Golden Ball winner.
After punctured lung in pre-season, he returned scoring 26 goals in 43 games Player Season.
“I would like to wish Paul all the best. This settlement enables him to take his time and find the right club for him, going forward, said manager Phil Parkinson.
“It can't be underestimated the role Mulls has played in the story of Wrexham Football Club over the last five years, with so many memorable goals and moments. He’ll be a player always remembered and revered by our supporters.”