Hi Cassie,
Firstly welcome to WAB.
Try this - open desired image in Paint
Click on image at top of the window
Then click on Attributes
In the box that appears delete the numbers that are in the two boxes
Type 800 in the width box & 600 in the height
Now click OK
Go to "file" at top of window and click save
Hopefully that should sort it out for you, you can of course put in whatever dimensions you like in the boxes.
Good luck.
Steve.
