If you want to know which version of MonoTouch you have installed you can find that in MonoDevelop using About MonoDevelop:
And click on Version information:
You can see that my Monotouch version is 5.2.12 which as of this writing is the latest stable version. But in case there is a feature you badly want in the beta / alpha version you can switch over to those quite easily.
Going Bleeding Edge
Just start MonoDevelop and go to Check for Updates as shown:
Next, now change your Update channel:
And you will be able to see the Beta / Alpha version available. If you like what you see. Just click on Switch Channel as shown:
It will start downloading and running the updates. Enjoy!