Children Book

I currently have an illustration saved as 8.5x11 and I need it to be 5.5x8.5. The file is missing requires bleed if I want my images to go off the page. I need it changed for Sure Print to make my children's book . Below link what SURE PRINT Requires for the bleed and margin.
https://sureprintanddesign.ca/article/how-to-set-up-margins-and-bleed/. My book is saved in a pdf form.