User blog comment:~Boggy B~/New Background/@comment-7697305-20150307220053/@comment-7697305-20150308001102

In GIMP, you can change an image's quality (ie. "compress" the image) by going to File --> Save As (or, if that doesn't work, Export As), changing the file's extension to .jpg, then clicking "Save" ("Export"). This will open a dialog with a slider which ranges from 0 - 100 (defaulting to 90). Check the box which says "Show preview in image window", then reduce the slider one point at a time until the file size displays lower than 300 KB. Then, once the image is saved/exported, you can view it to see if you are satisfied with how it turned out.