To change a recorded voice so that it sounds like an alien...

• Using Audacity, open the Recorded voice you wish to change
  
  Example of an original Voice Recording
• Move the mouse over the 'grey control section' at the start of the track, as shown here...
  
  ...and left-click...
  
  This is the quick way to select all of this track; the following image shows the result...
  Note: the change in colour showing the track has been selected.
• Either: Click on the Edit Menu and then select Duplicate
  
  
  OR use the keyboard shortcut Ctrl + D.
  Which ever you choose a second duplicated track will appear, like this...
  
  
  
• Click in the Work space to clear the selections from both tracks
  Note the change of colour again...
  
• Highlight the first track again then...
• Click on the Edit Menu and then select Duplicate OR use the keyboard shortcut Ctrl + D
  This will produce the third track required...
  Remember to clear the selection by clicking in the 'workspace'
  

• Highlight the first track (see above if you have forgotten how to select a track)
• Click on the Effect Menu and then select Change Pitch...
  
• On the dialog box that appears, change the Percent Change to 15 then Click OK
  
  
  
• Highlight the third track only (this may involve removing the selections then selecting the third track)
• As before, Click on the Effect Menu and then Change Pitch...
• This time change the Percent Change to -15 (just add the minus sign) then
• Click OK

Export the end product as an mp3. Example of the 'changed voice' - Alien enough for you?