How to enable apache module

i am using Prestashop on Webmin, but i need speed up my website. I have add some code to .htacces (mod_expires) but it not working. May be this module disable, can you help me to enable apache module for webmi. I am beginer and using windows, so i dont know to to enable this module. Hope you can help.
Some information of my sever

Operating system Debian Linux 6.0
Webmin version 1.740
Kernel and CPU Linux on i686
Processor information Intel® Xeon® CPU E5-2630 0 @ 2.30GHz, 2 cores