Cannot locate Package Manager window

I have just upgraded to Unity 2018.3 but I've run into a problem. I need to install a new package but I can't seem to find how to open the Package Manager window. In my last version of Unity it was in Window > Package Manager, that would bring up the dialogue. Now it doesn't appear to be anywhere. I might be blind but can someone help me? Thanks.

 

You probably have some fatal errors in the console (red ones), you need to fix them before you can open the PM. Unfortunately there are some errors which blocks PM to compile.

 

I fixed the errors and it still didn't come back. I then closed and reopened Unity and it's back. Thanks.