∴ rvm upgrade ruby-prefix [optional-source]

Attempts to install the latest version of a given ruby (still experimental).

Given a ruby prefix (e.g. 1.9.2), it attempts to upgrade your last installed
version, migrating gemsets.

The process will prompt you at each stage - if the versions look incorrect,
please cancel and perform it manually.

Examples:

If you have 1.9.2-rc2 installed and want to switch it to 1.9.2-p0,

  ∴ rvm upgrade 1.9.2
  
Will install 1.9.2-p0 and migrate the gemsets.