Replacing a toilet is a fairly straightforward part of bathroom remodeling.  It's only when a new toilet is being fitted in a different location that it can become more tricky, as soil pipes need to be moved or lengthened.  Most modern toilets have a close-coupled design, which means the cistern sits on top of the pan, and a benefit of this design is that it is simpler to install than conventional high or low level toilets.

If you're attempting to relocate your toilet to an internal wall, you will have more work to do.  In general, toilets are located on or near an external wall for a good reason - for easier access to the soil pipe.  It can be very difficult to fit a drainage pipe from a toilet on an internal wall, as it will be too large to run under the floor and would look unattractive if routed along the inside walls.  If relocating your toilet is essential to your bathroom's makeover, it's always best to keep it on an external wall if you can.

The first thing you'll need to do before you can install your new toilet is put together the internal cistern mechanism.  To do this, place the siphon unit inside the cistern and insert the threaded section at the bottom through the hole in the base of the cistern.  Slip the rubber gasket over the threaded section and move the connecting plate into place.  You'll need to use a large threaded collar and bolts to hold the connecting plate in position. 

Next, add the flushing mechanism or water control assembly into the cistern, passing the threaded end of the water supply pipe through the hole in the bottom of the cistern.  Use the washer or gasket supplied to fix it in position.  Tighten the collars for the supply pipe and siphon by hand.

Then, fit the flushing handle and double check that it's connected to the flushing mechanism.  Move your toilet pan gently into position, matching up the outlet pipe with the soil pipe.  Next, carefully lift the cistern up onto the pan, making sure the connecting bolts thread through the pan's retaining holes.  At this stage, you should put a gasket at the flush entrance and ensure the threaded section of the siphon unit is inserted through the gasket.

Using metal and rubber washers, secure the cistern in place by fitting nuts onto the connecting bolts.  Now it's time to use slip-joint pliers to connect up the cold water supply pipe to the cistern.  Once you've done this, screw the cistern against the wall, remembering to use metal and rubber washers.  Your cistern will probably come with pre-drilled holes in the back to enable you to do this.  You will also need to use retaining screws to hold the cistern firmly to the base of the pan.

The final job is to screw on the toilet seat, using the pre-drilled holes in the pan, and then switch the water back on.