This plugin has only one parameter, it is named 'Maximum Memory Size', by entering an integer number , say x, in this parameter, the plugin sets the memory limit to x MB for the whole joomla website.
The default value for this parameter if not set is 32.
So, after installation, you have to publish the plugin and set the 'Maximum Memory Size' parameter to an appropriate value.
Lets say your memory limit is set to 32 MB, you will increase this value by setting the parameter to 48 ,for example, to fix the problem.
Please read this article for more information:
Memory Limit Plugin (Joomla! 1.5 Native)
