how to change the memory limit in the class

when I use it on a linux server is sometimes gives
this error:

Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to
allocate 4796 bytes) in
httpdocs/includes/thumbnail.class.php on
line 312

Solution:

his is a memory limit error.

See the sample code in the line: (version 1.48 and +):
<?
$thumb->memory_limit='32M';
//[OPTIONAL] set maximun memory usage, (use '16M' or '32M' or ....)
?>

You can limit the memory usage, by default the memory limit in linux
php is 8MB (see php.ini), apply this line and adjust the memory limit
to your class