is it just as easy as downloading the newest source, uncompressing it, compiling it using the same (or comparable) options that were used on the last version?
That may work. Did you document the procedure? Have you built any PECL extensions, or compiled any other PHP modules, you may need to rebuild those.
Have you read the PHP changelog and upgrading notes to see if the is any notes from upstream that you should be aware of?
If you don't have good documentation about how you got the current version built/installed and what other changes you have made to the system then you really can't know for certain.
Just try building on a test machine, and test your applications. If everything works then that is what you needed to do.
If you don't have a test environment/VM, then build that first. If you don't have a backup system in place to revert your setup, if/when the upgrade on the production system fails, then setup that up right now. If you don't have documentation about how it was built the last time, then write it.
Is there anything that has to be removed or changed from the previous version installed?
Maybe, it depends a lot on what you did in the past.
Compiling on your own while clueless is a bad idea in my opinion. Are you subscribed to all the security lists? Do you have a strong reason why you aren't using a packaged version?
Have you considered using the package management tools on your system and building a local package? Building a local package is a good ideal.
- This is a form of documentation, since the control files can be put in a VCS.
- You will have a you a repeatable install, so you can test the exact same thing on your testing/dev/production boxes
If you don't want to figure out how to use the package tools for your OS, at least consider writing a script to perform the compile/install. That script will your documentation, and the one true source for the install procedure.