Go to the logos section within the Sven Co-op game files (they are probably here: C:\Program Files (x86)\Steam\steamapps\common\Sven Co-op\svencoop\logos). Right click one of the sprays and go to edit. Then simply draw what you want, but make sure the background is black without any kind of hue. Save it, and upon the next restart of Sven Co-op it will have overwritten the spray you choose to edit. Hope this guide came in useful, Enjoy!