Avatar maximum dimensions; width: 150 pixels, height: 150 pixels, file size: 97.66 KiB.
If you need to resize your images GIMP (GNU Image Manipulation Program)
is a great software for editing images.
Open GIMP.File > Open...
"choose your picture" (.jpg files are the best although the forum will recognize .gif and a couple other formats.)
When it opens from that window select: Image > Scale Image...
Select the width and height to 150 or less pixels (as long as it remains linked you can select the greater and it will proportionally adjust the other.)
Now go to File > Save as...
"choose your file name ending .jpg" choose the location to save and the file type "JPEG Image (*.jpg,*.jpeg,*.jpe)". A window will pop up. Select the quality (compression) you desire and click Save
Now go to your profile and upload the image as your Avatar.