So, if set my playerserver to support 1.8, can I set it to 1.12 afterwards? If not, is there a way I can completly delete it so I can get another one?
Yes you can, just visit https://playerservers.com/
and head over to the playerserver and go to the tab "Dashboard" and you can change the setting named "Server Version". Otherwise, if you would like to reset your playerserver, just go into the lobby and type "/reset <playerserver>"</playerserver>