How do I install a performance cooling fan?

I was going to replace my cooling fan to get a little better performance. I was wondering if anyone has done this before and if spacers were needed (how big, if any), if this is a clutch fan, and how big the stock fan is (to get a size on a new one). If anyone has done this before and can tell me exactly what i need and how to do it, that'd be great, but any help is always welcome.

thanks.