It's been a while since I did it, but after you've checked the codes, wait at least two seconds, then you hold the button down for six seconds. Each code must be erased individually.
If it doesn't work, contact Arthur Dalton. He is the fault code guru.
Code #5 is probably the most common fault code on this engine. It thinks your EGR valve is stuck shut.
There was a TSB on the EGR valves, and the older valves had a tendency to stick, so it might be a good idea to install a new one.
Additionaly, the hot inlet pipe to the intake manifold gets clogged up with carbon from the egr vapors.
Stevebfl, Steve Brotherton, wrote an article that is posted on this site:
Scroll down to the end of the article. There are pictures. You clean out this egr tube with something like a speedometer cable attached to a drill motor.
I'm willing to bet this tube is completely blocked. It should be cleaned out at intervals of 60,000 miles.