Do I really need Desoldering for replacing resistors/caps?

You can use old solder, but fresh one is always better.
If you spot cold solder joints or cracked with magnifying glass, than you simply can re-touch the old one .
try to go http://www.parts-express.com/cat/desoldering-tools/520 and choose 45W desoldering iron.

Thank you very much.  Any good solder you recommend?  I have a Kester 66/285.

I use Weller, but it’s hard to find. Had purchased mine 10 years ago 4lb.
I would not recommend neither tin or ones with silver added. Make sure you're bellow 200-Celcius range of melting Will be impossible to work and will require high heat which you often don’t want to use on circuit boards.

Thank you very much czarivey. Really appreciated your help Sir.
Eddy

You could get manual desoldering pump for $4.50 or solder wick 
http://www.parts-express.com/Search.aspx?keyword=solder%20wick&sitesearch=true
Kester #66/285 is a proper solder - eutectic Sn63/Pb37 is the best for small electronic parts while 285 flux is mild and can be left on the board.