nelo theme - custom homepage

We've accidentally uploaded to crop a very large image file into the area for the left hand custom sub image area in the custom homepage. I can see the image and move the crop area around, but when I try to set thumbnail I get the following fatal error:

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 15552 bytes) in /home/enen7462/public_html/wp-content/themes/wpmu-nelo/lib/functions/options-functions.php on line 1331

I don't have any options to delete the image or change it to a new and resized image.

Any hints on how to reset this area?