Need Help Upgrading PHP...

OS Platform/Applications: --------------------------- Windows 2000 Server IIS 5.0 PHP 4.0.6 MYSQL 3.23.x Questions: ----------- Ok, I am debating upgrading my PHP version to the newest version, however since I run a pretty large webhosting facility and have several hundred domains hosted per server this is already a teadious task. What I want to do is make it as hassle free as possible. I have never upgraded PHP, so this question is simple "How Do I upgrade PHP on Windows?", and "How can I maintain the integrity of the PHP sites hosted?". Is this a difficult process? Do I uninstall the old php, then install the new one? Or Do I just use the install file over-top of the old one? Is it safe to go from version 4.0.6 to version 4.3.x? Are there any special procedures about upgrading that I should be aware of? Conclusion: ------------- Any help in this is greatly appreciated! --Thanks, Tony D. P.S. this is a repost, no one answered my previous post..