Updating PHP from version PHP 4.4.4-8+etch6 (cli) to PHP 5+ ??

Anyone here who knows if it's easy to update PHP from version 4.4.4-8+etch6 (cli) to the last stable 5 version?
I'm using the 'old' version on my Debian Etch server (running ISPconfig), and would like to update to the new version without breaking to many things :-/

 

ispconfig runs its own php binary I thought... so you could simply update php4 for php5

 

That's right, you can simply use apt to update PHP. But you should check if your PHP applications are compatible with PHP5 before you do this.