I have been messing around on lots of forums for donkeys years, and have tried many different ways of reducing image size, the simplest method of doing it is by installing windows image resizer
This tool used to be part of the original "power toys" that was a genuine windows download, that had been discontinued for many years, but power toys are now re-introduced but if you dont want to download power toys, and you just want image resizer alone can be downloaded here
https://www.bricelam.net/ImageResizer/
It is so simple to use one installed all you need to do is drag your cursor over the images you want to resize right click the selected images and press the resize option in the right click menu
Three mouse clicks can resize 1 image or a hundred images
I made a rubbish quality video
see link below to show how simple it is to use, i really dont see it could be any simplier 
please notice on the video there are two extra steps shown, i show the properties of the images before and after 28.5mb resized down to 1.53mb
i always resize to large fits on forum pages no probs, and i also dont have the create duplicates ticked, i find it gets a bit messy if that is left unticked
https://www.youtube.com/watch?v=HTsj0-LTZTs
edit, once you install the programme "resize images" will be added to your right mouse click menu by default, so there is no setup other than installing.