It's not a difficult task to replace an old toilet, as long as you can connect it to an existing branch of the soil pipe. You can cut your water usage significantly by fitting a dual flush toilet mechanism.
Follow the manual's guidelines, assemble and insert the flush mechanism. Make sure you include the rubber sealing rings where necessary.
Place the large rubber gasket into the flush ingang of the pan.
Insert the bolts through the holes in the cistern, using the rubber and large metal washers supplied.
Lift the cistern into the pan so the connecting bolts fit through the holes. The threaded section of the flush mechanism should go through the rubber gasket on the flush entrance of the pan.
Fit washers to the connecting bolts, and tighten the wing nuts. Make sure you fit these securely - but don't over-tighten them.
check if there are no either pipes or cables below the fixing points. Put the toilet in place, and slide the pan outlet into the flexible connector that's attached to the soil pipe. Then drill some pilot holes into the floor at the fixing points. If it's a solid floor, you'll need to make the holes with a hammer-action drill and plug them.
Push plastic protective inserts through the holes in the base of the pan, and insert the retaining screws through and into the floor. If the cistern has fixing holes in the back, attach it to the wall by drilling and plugging. Remember to add rubber washers before you tighten the nuts.
Connect the supply pipe for the cold water feed, using a push-fit tap connector.
Fit the hinge assembly to the seat, following the manufacturer's instructions.
Connect the seat to the pan by securing through the holes at the back, using the screws supplied. Then adjust it to sit in the correct position.