How to reinstall software you have paid for/bought

To reinstall purchases that you made in a previous Ubuntu installation: 

• Open the software Centre
• From the “File” menu, choose “Reinstall Previous Purchases”.

• If prompted, sign in to your Ubuntu Single Sign-On account.

• Select a title, click it, and click “More Info”.

• Click “Install”.

If this does not work, there is also a fallback method:

• Go to https://software-center.ubuntu.com/subscriptions/ in your favorite web browser.  
   
• Click a title.

• Copy the “deb https...” line and add it to your system's software sources. There are a couple ways to do this:
  • - Command line:
    1. Start a terminal. b. Obtain root privileges by running 'sudo bash'. c. Using your favorite text editor, paste the deb line (as one line) at the end of a file called /etc/apt/sources.list d. Run "apt-get update".
    - Update Manager:
    1. Run update-manager, or invoke it from the software update icon at the top of the screen. b. Click "Settings...", and enter your password. c. Click "Other Software". d. Click "Add..." e. Paste the deb line into the dialog box. f. Click "Add Source". g. Click "Close". h. If prompted, click "Reload".
    2. Close Update Manager.
• Install the software, using synaptic (GUI) or apt-get (command line).