upgrade DDOS and DD Boost license DPS

Hi All,

I would like to ask DDOS and DDBoost license upgrade.
Now customer environment as follows,
DDOS version 5.4
DD Boost license (Legacy model)

The customer wants to upgrade their DDOS from 5.4 to 6.2.
Then I have some questions.

(1)If upgrading DDOS from 5.4 to 6.2, do we need to renew the DD Boost license?
Or can we keep and use the current version DD Boost license?

(2)DD Software has had a migration to ELMS(eLicense structure), so we want to make sure if we need to migrate to ELMS first.

(3)If we migrated DD Boost license to ELMS, can we still use this? Or do we need to buy DD Boost license?

Could some one please help me on this

Thank you,