Are you currently the Contract Owner? If yes, you can transfer this role to another Admin. See https://helpx.adobe.com/enterprise/using/change-contract-owner.html. If you're the only Admin, then you'll need to add an admin first. However, if you're not the Contract Owner then it's a bit complicated. (Scenario 2 in the above article)
While reducing the number of licences, I'm not sure if there is any option to cancel for any specific users. Ideally, we should unassign licences from user who no longer require them, and then reduce the licences. If all licences were assigned, I'm not sure what logic is followed to determine which ones are removed. Anyway, we're you able to reassign the licences to the corerct set of users?