How do I modify a .spec file

[mario chiari]

Hi

my first post, and I am newbie with rpm.
Very basic question: I wish to change a .spec file, how do i do?

I mean, I have a -.src.rpm package;  
it opens  as a -.src.tar.gz package and a -.spec file. 
I modify the .spec file (say, I  correct a path)
Now, how do I recreate an updated .rpm package?

Thanks Cheers
mario