Dave,
You rightly suggested Rosemary to copy and replace "Styles and Transitions" folder. Copy this folder from an old PC to a new PC.
PTE AV Studio should be closed when you replace this folder.
In future version 12 we'll add import & export commands to help with this task. PTE AV Studio will create a single ZIP archive. It also can be used to backup all styles and transitions and recover a broken storage to previous state by importing a previous copy.