Because of the need for audit trails, etc. it is not possible to delete function roles in SOLABS.
Roles that are no longer required, can either be re-used for another department (renamed with a new name representing this new department), or simply renamed to label them as obsolete.
For the latter, SOLABS also recommends to rename them so they will come at the end of the alphabetical order (ex.: zzz_Role1_obsolete). This way they will all be displayed at the end in Roles lists, reducing chances where users would continue selecting these roles by mistake.