If you are using Affnity Designer for your graphics design, often you are required to have “300 dpi” images, meaning your images are 300 dots per inch in resolution. You can manually change the dpi (resolution) of an image right in Affinity Designer. Here's a quick walkthrough on how to resize the image.
Affinity Designer is a graphics software solution (similar to Adobe Illustrator). I like Affinity Designer because you don't pay for a subscription; you just buy the software once and you own it forever. It's a great tool for creating vector files (and lots of other graphics projects).