GIMP2 Question: Help!

[Edrof]

Hi chaps, I'm sure this is a simple one but, alas, the answer eludes me.

I'm very new to image manipulation software and have recently created this book cover from scratch. I need the image to be saved at 300 DPI or above, and it must be a JPEG or a TFF. This is the error message I get when trying to upload the current cover image:

For best print quality, we recommend using images with at least 300 dots per inch (DPI). The current image has 72 DPI. Optimal print quality would be achieved with an image of 5.25 inches wide by 8.5 inches high that has at least 300 DPI.

I know how to save it as a JPEG or TFF, but when I try to fiddle about raising the DPI it seems to be stuck at 75. Google hasn't helped.

Any ideas about what I should be doing?

 

[Edrof]

The vector what now? Thanks Gord, I'll look into all that and then probably get confused and come back.

Cheers!