Access the Administration panel
First login to the project manager with your administrator account.
Click on your name and email on the top right corner to display a dropdown list, then click on Administration.

This will open a new window with the administration panel.
Change company of the administration
If you have access to more than one company, and you are administrator for these companies, you can change company on the admin. by clicking on the company name on the top-left corner.

Just select the company you want on the dropdown list.