I need to stop super mods from being able to delete threads
 

I want them to have all other functions except deleting how can I do that

thanks

Edit their usergroup's permission in your admin cp nad remove "can delete other's threads"(?) permission..

Better way:

Create a new usergroup for them and instead of revoking super mod's permissions, revoke your new groups's permissions according to your wishes and assign their names to this group.