Increase photo DPI using Gimp to upload for Kindle Direct Publishing

This video shows how to increase the DPI/dots per inch of a photo by: opening a photo in Gimp, scaling the photo by increasing width, height, and resolution (PPI/pixels per inch), and exporting the photo. It also shows how to change your preferences in Gimp to allow large image sizes.
I learned how to do this because I am publishing a colour print children's book on Amazon and even though I took photos of my paintings as HDR with my iPhone 6s, the resolution was too low for print.
This method works, but I still have a mystery -I am new to this and do not understand why the image, once scaled, is 171.5 megabytes in Gimp, but when I export it, it is 8.9 megabytes. Clearly is has something to do with changing from a .xcf file to a .jpg file.

[@marcosantibanez1895]

amazing worked for me!

[@samividhod]

Thanks for the video ...🙂

[@woodsmcleod]

You're welcome!

[@GrowingupWithKylie]

Thank you😅