Remove background for security badge

[BugsySiegel]

I am using a trial of Photoshop Elements 2022 with 29 days left. I know NOTHING about it and really only need it for one purpose. If I can make this work easily, I'll buy it!

I create security badges. I need to use submitted photos of various sizes, but I want to remove the background and replace with a neutral color (gray). Then I need to resize the photo to a specific pixel size (ie 300px x 400px). I searched but was unsuccessful in finding a simple way to do this. 

If someone has any suggestions, I'm all ears. Keep in mind, I have NO familiarity with PSE.

[Peru Bob]

Start here:

https://helpx.adobe.com/photoshop-elements/tutorials.html

and see here:

https://www.google.com/search?q=photoshop+elements+remove+background&rlz=1C1CHBF_enUS776US776&ei=ZV8...

Then Image > Resize > Image Size from the menu and choose your size.