Do I really need Desoldering for replacing resistors/caps?

Eddy, gs5556 obviously has experience with the very units you wish to modify. I would take his advice very seriously.

Soldering is not a very difficult skill, but it is a skill. I would not start on something which is towards the difficult end of the spectrum.

Soldering fumes are not that bad, but not that good, either. It would be a good idea to do it outside or with a fan sweeping the fumes away. Also, there are several types of solder - make sure that you are using a solder which is suitable for electronics (typically resin core), otherwise you risk corrosion which may kill your ARC.

Also, make sure that the solder sucker has a high temperature tip. Back in the day, some were made with teflon, which is not a good choice for anything more than 460 F, because teflon can begin to decompose at that temperature, and the decomposition products are bad, bad.

Don't want to put you off, because modifying good equipment is the best route to great equipment. But, it is a skill, and good equipment makes it a lot easier. If you are doing just the one piece, you might want to get a good tech to do it in his spare time. If he will let you watch, you can learn and take pride in being involved in the upgrade.

Sorry, meant to say, "But it is a skill, and good REWORK equipment makes it a lot easier."

+1 to grannyring. That's how I do it too!

Thank you very much everyone for many good advice.
Wow, I guess I will have to put a hold on recap, seem like very difficult to me. I guess I can do some resistors with no problem. 
Do I search for "Audio repair" online for a good qualify LOCAL tech do to recap for me or should I use any other words. I don’t really want to ship it to somewhere else if I don’t have to and also I can ask him if I can watch him while he do the job and can learn from him.

Eddy, in my home town the local high end store also does car audio. Their installer is superb - Mercedes quality or higher (and I own Mercedes).

I suggest that you visit a few car audio stores, and when you find the best, go into the shop and meet the installer(s). If you find someone you like, ask him if he could recommend someone to help you rework your ARC. You may well get lucky.