How to allow a local user to be an admin in Mac on AD?

Hey guys,

I have Windows Domain Controllers in an office, most users have Macs, a few users need local Administrator permissions, but when I go to users and Groups in Systems Preferences, that option is greyed out, I tried putting the user in the Administrative settings of AD in that Mac, but I don't know if that's the way to do it, so, did I miss something?

Thanks.