I have an issue RAM, SLOW EXECUTION

i am using openvz 512MB, 1gb burst

i installed virtualmin from script

so many unneeded modules may be installed, i think

in many website, i found that by using optimum needed apache module, it is possible to reduce apache process size to 12MB/process in prefork

because of installing too much script, NOW my server shows 45 to 50 MB/process, too much

i want to run only 1 vbulletin and 1 joomla

what are the module that much, please give me solution,

also can i convert preforke to worker for efficient mem utilization.? HOW

please give me solution.