Dunn, 26, has spent three seasons with the club but will join National League North side Curzon Ashton for the 2021-22 campaign.
Dunn was part of Paul Carden's squad that fell agonisingly short of promotion during the 2018-19 season, losing in the 'super play-off' to King's Lynn Town at Cantilever Park.
He made 47 appearances for the club, scoring 11 goals.
Defender Grogan returns to Radcliffe FC, and made eight appearances for the club after joining for the curtailed 2020/21 season.
Grogan previously made 132 appearances for Radcliffe before joining the Yellows, scoring 12 goals.