On the old computer, in Optitools Studio, click on Help > De-Activate Licence. Select Yes on the pop up box.
Then on the new computer, click on Help > Register for Licence. In the pop up box, click Register. Use the same IDL order code, contact details and email address on the registration form, and a new licence key will be automatically sent.
When the Licence key arrives, click on Help > Activate Licence and copy and paste in the Licence key.