Teach Me About Turbo Rebuilding

This is one of the few things I have yet to try or even attempt .  

Between this and engine building are two things I have never had a need to learn , do or even bother with. 

I was going to drop my two turbos off at the local shop to have them rebuilt but I am assuming if they can do it I can do it. 

What I have is . 

13t - Gen 1 

16t - P2 

What I would like to do is make them both 18t or something else if there is a bettter option for my 01XC 

So links ? Info ? What all is entailed to getting what I want ? 

Thanks