Instructions cover the following version upgrades:

  • When upgrading to 3.7.5.3
  • When upgrading “within” 3.7 itself (for example 3.7.5 to 3.7.5.3)
    • Specifically: If your wp e-commerce theme is still located at wp-content/plugins/wp-e-commerce/themes/ you should move it to wp-content/uploads/wpsc/themes/ in order to preserve your changes
  • When upgrading to 3.7 from any older 3.6 version

Read full instructions: http://getshopped.org/resources/docs/upgrades/staying-current/