How do you resize pictures on gimp?

When you have your desired image open, there will be a menu bar at the top beginning with drop-down options like "File", "Edit", "Select", etc. One of these menus is called "Image". Click this and you will see a list of options, including one called "Scale Image". Select this.

Once you have selected it, a "Scale Image" dialogue box will pop up. You can set it to a certain number of pixels or you can scale by percent, picas, inches, etc.

Note: By default, your image will scale evenly. That is to say, if you enter 50% as your X scale, your Y will automatically change to 50%. To stop this feature and distort the image by scaling on the X or the Y, click on the chain. It will appear unlinked once you have done so. To reverse this, just click it again and it will link.

Click OK when you have entered your desired scale size.

You're done!

I hope this has helped you. =]