Changing your saddle

You will need the next tools, depending on the shape of your bolt in your seatpost. The bolt is situated under your saddle

Allen key

Wrench tool

Unscrew the bolt completely

After removing the screw, remove the top part of your seatpost

Now, you can remove your old saddle and put the new one. Be careful to keep the down piece (in red) of your seatpost in the same position. It is recommendable to apply some lubricant (grease) on the saddle rails and in between the pieces of the seatpost, to avoid noises

Put back the top part of your seatpost (in red) and the screw. Screw it but not completely, you still need to be able to adjust your saddle in the next step

With the help of a level tool, put your saddle in horizontal position. The bubble inside your level tool will be in the middle when your saddle is horizontal 

Once your saddle is in the right position, screw completely the bolt in your seatpost and clean the rests of the grease you applied before to avoid noises