At some point you will have to replace the bar and chain on your chainsaw. The steps are pretty much the same for all brands. Here is quick look at how it's done:

1- Make sure the saw is not HOT 
2- Disengage the safety brake. (don't forget!)
3- Remove the bar cover nut(s)
4- Clean debris from cover and surrounding area
5- Put the new bar on and new chain over it with cutting teeth facing forward.
6- Install bar cover and hand tighten the nut(s)
7- Use the adjuster screw to give tension to the chain
8- Tighten the cover nut(s)

Helpful tips:
- Use the right chain by matching the: Gauge, Pitch, & number of Drive links.
- Flip bar after installing new chain
- Wear gloves and eye protection