Can I add more space to a partition after it's created?

Hey, first of all, sorry for the 3rd thread in a row. I promise it's the last one haha.

I installed windows 7 on a separate partition using Bootcamp.
Thing is, I changed my mind and I want to add more space to this partition. Is there any way of doing this?

Also, now that I have Windows 7 installed. How do I change from one to another? I thought there would be an option at startup but it just goes straight to OSX

Thank you