I'm not a plumber, but I have to say that this is one case where I do think you should actually hire one. I know that may seem expensive, but let's say you do it yourself and mess it up. Then you might have to hire someone to come fix it and it might cost even more. Better safe than sorry.
I wouldn't want you to be injured or cause damage to something when attempting to solder if you are not confident in your soldering abilities.
If you insist on soldering, please make sure that you practice on some scrap or something first to make sure you have the technique down.
That said, I still think you should go with a professional. Its possible that a licensed professional may actually be required in order for that work to be done legally, but I'm not certain what the rules are where you live.