How to change Ruby version using RVM

RVM stands for Ruby Version Manager – it's a program that allows you to install and run different versions of Ruby and Rails on the same computer.

So, here are the main commands for viewing the current Ruby version and switching to another version using RVM:

To view all installed versions and the version you currently have, open a terminal (Ctrl+Alt+T) and run:
```
rvm list
```
To change the Ruby version, run the rvm use command with the desired version, for example:
```
rvm use ruby-1.9.3-p448
```
To set a Ruby version as the default, run the rvm --default use command with the desired version:
```
rvm --default use ruby-1.9.3-p448
```