You can currently connect one CRM per account (Pipedrive, Salesforce, Copper, or HubSpot CRM), but there is no limit on how many marketing tools you can connect.
That said, it is possible to replace the existing account with a new one by navigating to account settings and clicking on “Reconnect”.
P.S. Before reconnecting, make sure you are logged in with the new account you want to connect in your web browser.