Upgrading is just a matter of compiling and installing 5.20, however the problem isn't whether you can upgrade or not it's whether you will break sites with the upgrade. I am pretty sure you will so I haven't been brave enough to tried it. Is 5.20 an option in the newest easyapache script?
IF you really know what you are doing you could goto Hardened-PHP and get the patch for the htmlentities overflow and apply it to the php 4.4.4 source. I don't know how easy that would be to implement into easyapache though.
