If reg option is not available, it means that your product is registered.
But you can always re-register your copy.
You should clean Registry Editor with the following instructions:
1. Start button-> Run command
2. In the field enter "regedit" command
3. Open "HKEY_CURRENT_USER" and select "Software" item
4. Find DMSoft Technologies folder, open it
5. Here ‘product name’ folder must be presented
6. Delete ‘product name’ folder
7. Open converter again afterwards and register it with new data.