Fatal Error

Hi guys . I making singleplayer game . But when i played game , this window pops-up . What can id do ? Please help me to fix this problem.

Unity is out of memory. Reboot the machine, then start Unity again. If it continues to crash, then you’ll need to reduce the amount of memory your game needs. The easiest way to do this is resize your textures by 50% in Photoshop or Gimp or whatever package you use.