Should I upgrade my server?

[GreyFilm]

Hey my site is hosted by siteground.com and my server supports PHP5 but you have to upgrade from the earlier version of PHP to get it and it cost $30. The only time I use PHP is for user authentication (Client Login Form), should I upgrade to PHP5 or are my fine with the version I have now.

[thorpe]

If what you have is working for you, then thats fine. php5 introduces a few new OOP features, but if you dont miss them you probably dont need them huh?