I am on Windows 10 and double-clicking on a photo, in the directory, opens it in Photos and allows me to crop the picture and re-save or save as a new file.
Or Open in Paint and I can resize it to the requuired number of pixels - usually 1500 wide, then save or save as a new file.
I have to admit that loading programmes and so forth totally baffles me - just been loading a programne called Zoom so that we can do video-links with our daughter and family - don't know yet if it will work!