Removing an old bath, taps and waste trap:
Place a screwdriver end inside the opening of the bath tap and using this leverage with another hand on the top of the tap turn anti-clockwise to wind it off and out of the inside the wall wingback elbow. Then repeat for second tap. If there is not enough room to swing the tap around undo the head works of the tap by removing the top indicator dial and unscrewing the tap body etc. Next go underneath the bath and remove the trap from the end of the waste pipe. If the trap is made of copper or lead and there is no visible thread on the outlet side of the trap just cut this waste pipe some ways back towards its outflow into the main drain. If you cannot physically get under the floor below the bath remove the paneling skirt around the bath and run the top of the trap through with a hacksaw with a 32 teeth to the inch blade. Or if you can undo the top trap nut where it meets the bottom of the plug and washer on the bath than do this.
Now break the entire baths frame accessible and remove bath by first removing wall board above bath as necessary. Now with the bath removed you will be able to get your first good look at what the existing hot and cold water pipes are made of and their respective sizing. If you find galvanized steel piping and you have a concrete floor do not worry. You will be able to purchase a coupling with a rubber seal that can go over the galv pipe down low about 4-inches (100 millimeters) above the floor where you are about to cut them with either a hacksaw with a 24-teeth to the inch blade or the use of a battery or electric sabre saw to ease the workload. However if your new plans allow you another position of your water pipes to begin the running of your new poly pipe work. Then work out how far back into the wall these galv wingback tap outlet elbows are as you may be in a position to block these pipes off at the elbows for good.
If you find your pipe work is in copper. Also cut them both about 4 inches (100 millimeters) above the floor level. And remove the screws and the remaining brass wingbacks that the taps were screwed into.
Please note: If the copper pipe is bent or out of perfect roundness anywhere near the cut off point then relocate your cut to further up the pipe then 4 inches above the floor.
Generally you will find two different sized pipes used a ¾-inch (20 mm) for the hot and a ½-inch (15 mm) for the cold line. Whatever you find is ok. There is also the chance of uncovering and striking an unknown pipe type made out of either black or grey plastic. In these cases do not cut the piping until you can establish at your plumbers merchant if they have a comparable match for it to allow an adaptor- fitting set-up for this older piping. If worst comes to worst. You will simply have to use the standard industry threads inside where you removed the old tap ware. Still being either ½-inch or ¾-inch threading. And if coming off this older piping to either place wingbacks for a new bath position or you are upgrading to a stand up shower or relocating or placing a toilet or vanity or pedestal basin. Either way there is an adaptor set up you can use. It just pays to seek out the options each existing water piping material gives you before rushing in at it.