Bottom line is that you can't reduce size while maintaining info (quality)
Some image formats are more efficent than others.
Try saving the image as a jpg if you are currently saving it as a bmp.
You can also save as different "colour depths".
I don't know what you are using to edit your pics
I usually just use MS paint or MS photo editor, just cause they are there.
You can probably save the image as 8 bit colour rather than true colour.
Check in properties or image options or something like that.
Save one copy of the image somewhere safe
Often there are settings for:
Changing any of these can reduce the size of the image
The smaller the image, the worse the quality (generally speaking)
The trick is just finding a compromise you can live with.
Computer experts are just people who are not afraid to screw around with them until the machines do what they want.
If life was easy, everybody would have one...