Step 9: Desoldering old DC power jack
Desolder your old DC jack following the This Guide "How To Desolder Components""How To Desolder Components"
Another and much better guide to desolder and re-solder a power jack is DC power jack repair guide. Do-it-yourself instructions. The credit goes to Laptop Freak.
I did not use desoldering pump. Instead, I bought desoldering braid from RadioShack for about $5. Soldering before desoldering works pretty well, though.