Help in PHP - Out of Memory - Almost giving up!

Dear team, how are you?

First sorry for the apelative subject but I searched around all the internet and I can't find the solution, and I'm desperate.

My problem is, I have a VPS unmanaged and I can't run a joomla and a magento website because of Out of Memory, all of this after I change the 'php.ini memory limit' of de 32m (default) to 256m. After a day the website work normally, but after this, these 2 websites (only 2 I using in server) are showing this error:

comprajogos.com.br (using magento system)
Fatal error: Out of memory (allocated 2883584) (tried to allocate 30720 bytes) in /home/comprajo/public_html/lib/Zend/Cache/Backend/File.php on line 246

Here you can find my PHP details:
comprajogos.com.br/test.php

Other site showing the same problem:
brazilarmy.com.br (using joomla system)

So guys I don't know what to do. If you can help me I'll appreciate.

Thanks in advance.

Regards

Luiz Henrique