Photo help Jpeg size

Usually the problem is the other way round i.e. file size restrictions require you to reduce your file in size

Have a look here

https://m.wikihow.com/Resize-a-JPEG

The windows paint option looks easy enough, allowing you to make the file a little bit bigger by resizing.

Right click on image and open with paint.
Click on resize button somewhere in the top tab/menu
Change the percentage from 100 to 120 or 150 and the size will increase accordingly.

thx both

https://www.photoenlarger.com/

Just Upload,  Enlarge  ,Right click and save

Brilliant free Site for doing anything With Images

Somewhere on here may be the solution to my own problem!

One of my own paintings is physically 750 x 750 and is in my gallery, and obviously was recognised to be an acceptable size in KBs...

I decided to adjust, and add some detail, but now told it needs to be at least ??? (can't just recall at the mo), but the question is why!

I will be working through these solutions later......