Rooftree, MS has free photo editing software that is very easy to use, Microsoft Office Picture Manager, which I use on Win 7. I do a 'save as' to save the resized file and just add RS to the filename, this maintains your original. There is also software that does not change your original, but this software is a bit more involved; it is called Lightroom from Adobe and it costs a bit of change.
If you have a copy of Office 2007, Picture Manager is on there. Folks have loaded it to Win 10 and say it does work. There is nothing similar on Win 10, however, there are free resizing software available, just use caution and do diligent research before downloading.
This is the link to the free Microsoft resizer for Win 10; they re now called 'apps'