BuddyPress.org

Change the value you need in your php.ini file (if you have acces to this file on your server)
on your server under memory_limit=
Below is my actual configuration for my buddypress site

;;;;;;;;;;;;;;;;;;;
; Resource Limits ;
;;;;;;;;;;;;;;;;;;;

max_execution_time = 60 ; Maximum execution time of each script, in seconds
max_input_time = 60 ; Maximum amount of time each script may spend parsing request data
memory_limit = 256M ; Maximum amount of memory a script may consume