Webmail error

Hello. I have a problem with my mail, i can see on cPanel that i ran out of memory, i tried to erase emails from the webmail section but this error message appears Error de servidor: STATUS: Internal error occurred. Refer to server log for more information. [2018-04-09 21:14:32] (0.009 + 0.000 + 0.008 secs). I don't know how to fix the problem or buy more space. Can you help me