Well there is more than one way of course, closely related.
1. Before you pull the old belt off get some obvious marker and mark the old belt across the pulley (both of them) plus the crank pulley.
OR
you can rely on the markers in the cam pulleys, most factory ones will have two holes that you can look through and line up these markers on the block, of course you can kind of do both. But you need to be sure.
2. Then pull the belt off and have a look at it's condition by bending in back on itself
3. To get the pulleys off there should be some sort of key on the shafts and then just pull them off, you may need a rattle gun or bit of pipe (extra leverage) on an socket handle or other tool for the crank pulley nut(use assembly lube or copper coat when you put it all back as this will make it heaps easier the next time).
4. The front seals kind of get killed here as I use a screwdriver to dig into the seal and lever them out - your replacing them anyway
5. Put a bit of grease around the new bearings to help them slide into place and then push them into the bearing seat, try your best not to force anything. It is important to try and put them in square. might need to use a urethane mallet just to tap them a bit.
6. Put all the pulleys back into place, spinning everything into the right relational places.
7. Now you can rely on the markings to align everything or you can line up the two belts and copy the marks made on the old one to the new one. Then with these markings line up the marks made on the pulleys and dah dar!
Pictures would help this make more sense, but anyway....