The industry image needs to be at 300dpi and 2625px wide by 1025px tall. That's the dimensions allocated to each media type and the requirements for printing with utmost clarity, so even the largest items come out looking fantastic!
If you are having trouble editing the image, you can download GIMP for free or head over to Fiverr and find someone to edit the image for you.
How to Rebuild the Media Center
How Do I Print Postcards and Business Cards
Do I Need to / Can I Give My Clients Access to the Media Center