2001 nissan altima

The light of "Engine serving soon" is on on the front panel. went to Autozone and asked for check

the problem. The detail content as following:
Troubleshooting P0304

Definition:
Cylinder misfire detected-Cylinder number 4

Explanation:
The powertrain control module monitors the crankshaft speed and has detected a misfire condition

Probable causes:
1. Ignition system fault-spark plug(s), ignition wires,
2. Vacuum leak,
3. Injector fault,
4. High or low fuel pressure.

The light has been on for months. when I wait for on the red light and pedal the break, I feel the

car trying to push out although I break it and it is viberating more than before.

Is it a big problem? If I try to fix it by myself, is there a probability and what is the

procedure? Thank you!

Ganou