Cropping & Resizing under GIMP for Windows
Continued from the GAP guide edition.
To crop and/or resize all frames automatically, under the Layers window, select layer frame_000001 (Or the lowest layer) by selecting it with a left-click of the mouse.
Select the Crop tool form the main GIMP window. Click on the image using your left-mouse button to bring up a Crop & Resize window. Within that Crop & Resize window, Origin X & Y will indicate the top left position of the crop plain. Height & Width will indicate the bottom right position of the crop plain. Select Crop when done to crop the image. Crop will also resize the canvas plain to the new crop points.
To resize the image, right-click on the image and then select (Image/Scale Image...). Within the Scale Image window, all that is needed here is to adjust the Pixel Dimensions. There you adjust the New Width and Height. Then select OK when done.