"I have no time" or "I don"t know how to do" or vice versa or both

I've already posted how to do it with a smartphone or tablet, using free apps like Photo-resizer.
Here is how to make your life much better under MS Windows.
Download the free Microsoft Powertoys from here: https://github.com/microsoft/PowerToys/releases/
The current version is show here :
Execute the program to install to Powertoys tools.
Reboot your PC.
Once rebooted you will have new contextual options when you right click on an image file or on multiple selected photos like this :
Select your image or set of image and right click then select Resize pictures:
You will see these options :
If you want to be sure to be able to upload that photo on the G503 forum, use the Small option.
Powertoys will then resize the photos to a size < 256Kb required in a breeze, keeping the originals.
You just have to use the resized photos in your posts on G503.
That's it.
FINE TUNING ONCE FOR ALL
If you want to adjust the default size corresponding to Small or Medium of whatever so that it's much closer to the maximum allowed size on G503,
click on the Powertoys icon in the lower left part of your windows desktop like this:
Play with the options as shown in the Powertoys options Window:
If you want to get rid of the resized photos after having completed your post on G503, that's easy:
Each resized photo was renamed with the size marker, like this xxxxxxx(Small).jpg
Just select each photo with the (Small) trailer and delete them.
Hope it will help G503 user using MS Windows.