You can convert the PNG image to a JPG in your image editor. PNG is a better format than JPG, anyway. They are lossless and support transparency while JPGs are lossy and don’t support transparency.
You must be looking at a tutorial for the desktop version of SketchUp. Currently you can’t edit materials in SketchUp Free.
Not specifically. SketchUp 2017 Make is available and like SketchUp Free, it’s licensed for non-commercial use only. Since you are using SketchUp for your business, you must be using SketchUp Pro or SketchUp Shop. With SketchUp Pro you would be able to export JPGs and you would be able to edit materials and create your own materials.
Thought PNG was mainly for Illustrator and vectors but it makes sense and I have just tried importing and editing a PNG shot from SketchUp in Photoshop and it works just fine. Thanks!
For reference, png (portable network graphics) is a lossless file format for images. It works well with technical images because it does not attempt to compress them. jpg is a format that reduces the size of an image file by means of a lossy compression technique. It works well for scenes of natural objects because the eye tolerates some loss of details. But it often works poorly for technical images because the fine details matter.