Hi, your theme includes a modified version of Visual Composer and you will NOT be able to use your theme license code to register Visual Composer itself. Registration of VC is also not necessary, as it is fully functional without.
And because you received VC as part of your theme, you will also NOT be able to use VC’s auto-update routine, as that feature is in fact reserved for direct buyers of VC only. You will receive all VC updates through the theme author, whenever a theme update is released.
If you want to use VC’s auto-update and/or also receive support for VC directly from the VC author, you should consider purchasing an actual license for VC yourself. But as long as you are using the modified VC version within your theme, the theme author is responsible for providing you with updates and support regarding VC.