This is one of those things... if you do it yourself be prepared as you may end up breaking the glass, if there are any cracks or chips on the window it could break during install. This is why many places will install used glass but will not guarantee it.
You need help with this. Two other people is best.
Suction cups for the glass, it is possible to do without but holding onto the glass can be tricky, and tricky is not a good in the same sentence as glass.
1) pull the old sealing strip out of the window, start with the metal jointing bits.
2) spray some 50%/50% dish-soap/water mix in the seal where the glass sits, lift the flap of the seal and spray it inside, this should allow the glass to slip rather than pop out.
3) use the suction cups to pull the glass while other helpers are massaging prying the glass at the seal. Don't use metal to pry. If you don't have cups, get someone on the inside to gently push the back side of the window outward, while you work the top of the glass, get the other helper to work the other side top of the glass. Once you work the top out move slowly around the rest to get it out.
4) Clean under the old seal. Rust can develop here.
5) put new or used seal back on, use some rtv or other silicone sealant over any repaired areas.
6) install window reverse of removal. be sure to lube up the whole seal where the window goes. It's best not to do this in the sun, if you can keep it moist it slips in better.......
7) Install new sealing strip, make sure you position it center from the start or you'll have to pull it off again. Some guys use a string, and lay it in the seal then proceed to pull the string as they work the sealing strip in. It's hard to explain, the ultimate goal is getting the sealing strip into the seal without damaging the sealing strip.
8) with the ends of the sealing strip lifted out of the seal, put each end of the sealing strip into the metal jointing bit. You then need to push the metal bit into the seal as you have done with the rest of the sealing strip.
That's how I've done it. I hope this helps.