I am mailing 3 books, 3 book for 2 credit deal.  It came up as bulk, first class.  I just received 3 books  mailed media, which i believe is cheaper.  How do I get the wrapper to print media mail and not first class.  If its cheaper, can I just cross off first class and still mail it as media?

yes, just cross off the first class.  write media instead.

I've had books weighed at the PO and it came out cheaper to send them differently than how the wrapper printed and the postal clerk marked it out with a black permanent marker.  Of course they have a stamp for First Class or Media Mail, but you could just write it on the package.

Ok, thanks.

My post office puts a little sticky label on top and then stamps the label.