General Questions.

If you want to upscale 4K footage, you need to drop this in a 1080p project. You can upscale to 100%.

Provided, the timeline is not set to Scale to Framesize. Image will be set at 50% on the timeline.

If your 4K footage is in a 4K project, then any upscaling will cause image quality loss. I would not go past 110%.

When Premiere Elements is open, it is always in an open project with a default name like "New Project".  So, the right place to start is with "File → New → Project" so you can give it an appropriate name like "Montana Wildlife".  

The next important thing to do within that named project is to slide a first typical source clip to the timeline.  Premiere Elements looks at it and creates project settings to match for best quality.  You can later move it or delete it.  You can also do this manually through the New Project dialog, but it is probably easier and more accurate to let the settings establish automatically. 

"Motion/Scale" is my choice for "zooming" or "enlarging".   It does not work as good as with still photography because of the limited pixels.   Another way to "Scale" is selecting the clip and double clicking in the preview window.  Round "handles" will appear.  

If your footage is "HD" (1920x1080) image quality will degrade rapidly when scaling for a HD project to be seen on typical HD screens.  If you should 4K, you have twice height and width, so 2X scaling in an HD project is usually workable.  In the end, you get to decide when the visual quality is sufficient.   

My "best way of doing that" is to always shoot 4K and usually edit in projects set to HD, 1920x1080.  It works well for computer viewing through YouTube, Vimeo etc.   If your plan is to view on a large 4K TV, there are other considerations!