I would word it this way:
---
Netbeans 8.1 comes with a new version of JUnit (4.12) which requires the "hamcrest" matchers library. [This library was bundled with previous versions of JUnit.] or [This is a new library dependency for this version of JUnit.] Click the resolve button to automatically add hamcrest as your project's test dependency. Or, if this project does not use JUnit, you may manually remove the JUnit library from Project Properties -> Libraries -> Compile Tests.
---
The reason I think this is necessary: I am a very experienced developer, yet I had to guess at what "hamcrest" was and what I needed to do about it. I guessed correctly, but less experienced developers might not not understand at all.