So I am currently travelling abroad through Europe. I'm using my friends laptop and hence his itunes for music. I can add songs onto my iphone which is a 3GS but I can't delete them. If I right click it only comes up with 'get info' and I'vew tried going to edit and hitting delete but it's not available to press. I've also tried hitting the delete button on the keyboard which also does not work. Help please?

You probably didn't authorize your PC to make changes to the I-phone.

How do I go about doing that?