Each instance has an owner. This is the master user who is ultimately responsible for the instance. If you are on a Team or Enterprise plan you can invite other users to the instance too. If you need to transfer ownership of the instance to another user (for instance if you are leaving a company or organisation) you can do that as long as the proposed new owner agrees.
To do this go to the Settings Section of MyMalcolm, within the instance you wish to transfer ownership of. Navigate to Ownership.
Remember that billing belongs to an instance so you may wish to update the billing details of an instance before you transfer it to someone else.