Discovering/updating component file versions in maven dependencies

I'm a new Maven user, using it almost completely through Eclipse.
I've installed Nexus as a repository manager. It all works.

1. Suppose I set up a dependency today, say on "needed-component". I
have to explicitly reference the specific version I want, say
"needed-component-2.3.4". I had hoped there would be a way to just
make a dependency to "needed-component" and have Maven keep me up to
date with the latest version, but I gather that's not the Maven
concept. Am I overlooking something?

2. OK so I have the explicit dependency to "needed-component-2.3.4",
set up using Properties->Maven->Add Dependency, finding the most
recent version in central, etc. Now is there any way to be notified
via Nexus/Maven/Eclipse when a newer version of needed-component
becomes available? Kind of a "check for component updates"?

3. Failing that, I suppose I have to survey repositories like central
myself and notice when new versions appear. OK so a year from now I
see "needed-component-3.0.3" is in central. Is there any way via maven
or maven/eclipse to update the original dependency, changing it from
"needed-component-2.3.4" to "needed-component-2.3.4"? Or do I have to
go in and edit the dependency spec in the project's pom.xml file
myself?

4. Eclipse/Maven has an Add Dependency capability. Suppose you make a
conceptual or typing mistake when adding a dependency and want to
revert. Why no symmetric Delete Dependency? Again, is pom.xml editing
the only recourse?

Thanks for any help.

- Les