How do I update my PHP version?

I know very little about php or how it works, but after hunting around for ages, I found a post about making a little file to run either phpinfo() or phpversion() commands to find what version I'm running. Apparently my account is still running PHP version 4.4.7 I'm trying to install some new components on my Joomla site, but I keep getting 500 errors & other various ones as the files attempt to copy across into Joomla, which (from what I've read) could have to do with trying to use php5 components on a php4 server. Is there a way for me update it, or is that something I need to request support to do for me? Next question - is there anything special I need to do with my site before/during upgrading?