I will be using the image below:

Open your image in Paintshop pro.

No go to Image > Resize or hit SHIFT+S in your keyboard.

A box will pop up. Now adjust the height or width with your desired size. If you want the image size to be proportioned, make sure Lock aspect ratio is checked. But if you want specific height and width unchecked it.

Click the OK button and you’re done!

Save your image!