Sure! Great question. I know there’s a tutorial somewhere in these forums and I hope somebody will provide you that. The quick answer is, you don’t. A PNG is a raster image file. It will always be a raster image file. You need to embed that raster image into a vector file (svg or pdf are, I believe, your current choices to use with your Glowforge). If you don’t have a vector editing app, you can purchase Adobe’s Illustrator or use one of many free tools out there. A popular free tool you’ll get lots of help with here on these forums is Inkscape. Anyway, that will allow you to place a vector shape where ever you’d like while also embedding your raster image within the file.
Hope that helps!
Edit: Here are a couple of posts that might give you some additional info on that… Additionally, do a search on “embedding an image” and you’ll likely find more.