If you wish to sell your Spark you need to make sure:
1. To transfer your license(s) on an USB-eLicenser, being resold to the next user
2. To delete the synth(s) registration(s) under your account: hhtp://www.arturia.com/login
3. To include all original elements in the pack: CD, manual, registration card
To answer your question, no you don't have to, at the second step, choose the product you want to unregister.
If still a problem with registration or any other question about eLiscenser, please contact :firstname.lastname@example.org