My b2evolution Version: Not Entered

Full error code:

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 43 bytes) in /home/geeksw5/public_html/blog/inc/files/model/_filecache.class.php on line 123

I know I need to increase the memory but I'm fairly uneducated on how to do so. Any suggestions on how I can do this are greatly appreciated.