I would like to increase the water flow in the bedroom area but the screws (original system) are completed rusted and can not move. Any advices? Is there a way to replace the old system?
Besides recommending extreme caution, I can also recommend Wurth Rostoff Extra as a much better version of WD40 or PB Blaster. Sold only online or at specialty stores.
I'm sure the valves can be replaced, but it should be done by a pro with the proper silver soldering tools (ie not your basic plumbing kit). I'm an avid DIYer but I'd call in a pro for this.