Upgrading to paid plan
Once your team is ready to upgrade, it is important to decide which team member is responsible for the subscription. The person in charge will have to be added to all team projects as one of the admins and project ownership will be set to this person's account. Once a project is owned by paid plan user, all the project users get access to according plan features.
To change project ownership, go to project settings and select Project owner in General tab. Note, that you can only switch owner to someone who has already subscribed.