Do I really need Desoldering for replacing resistors/caps?

Thank you czarivey.  The link you provided is does't work.  So it is not a good idea to use the old solder that left on circuit board after remove resistor?  

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