BROCK629 - hi, I'm not a plumber but I believe the screws/bolts you're describing aren't screwed into the concrete floor. They may be studs that were placed in the concrete when it was poured. You may have to do some destructive removal of those studs by breaking up the concrete enough to remove them. You may be able to find and install threaded inserts into the floor which the new bolts can be screwed into. These inserts would be secured with concrete patch or new concrete. Again, I'm not a plumber and hopefully, one of the expert plumbers who routinely post here will either confirm my approach is correct, or will give you the most cost-effective & DIY-friendly way to make the repairs. Good luck - regards! Jim D/West Point, VA