The installation process is the same as previous of Unity
You will need to update both the Editor and the DevAssistant (the PSM ToolSet is unchanged).
If there is a mismatch (only updating one or the other) then this will result in an error message when trying to launch the application ("Application is using an unknown runtime version")
Direct links for the Hotfix2 Release
Unity Editor 4.3.7p3 with PSM build option incl. the updated hotfix, MonoDevelop and offline PSM documentation:
PSM Tool Set for Unity 126.96.36.199 (no changes, same as before) (PSM sign-in required):
Development Assistant for Unity v1.06 (PS Vita application)
http://bit.ly/psmdevapp (Use PS Vita's web browser to download).
Online "Unity for PSM" documentation