Change the administration services service account in ActiveRoles Server is required.
In a very basic configuration, changing it in the Services.msc should suffice, along with placing it in the Local Adminstrators group. Please check to see if any of the Managed Domains is configured to use the service account information or if it's configured to use a username and password specified.
If Active Roles is configured to use Windows Authentication, the new service account also needs to have appropriate database access.
The ARS Quick Start Guide provides further details when setting an ARS service account:
1.- Administrative access to the computer running the Administration service.
2.- Publish the Administration service in AD.
3.- Access a corresponding Managed Domain.