You'll need to edit your php.ini file settings to something like
max_execution_time = 30 ; 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 = 128M ; Maximum amount of memory a script may consume (8MB)
or to temporarily up your limits edit your includes/config.php file and add these lines right under the <?php line:
ini_set('memory_limit', 128 * 1024 * 1024);
You may need to change the 128 to 256 or 512
See if that helps