Although it’s pedantic, you can’t technically cancel a Registered Agent, since you always need to have a Registered Agent listed with the state.
If you want to name a different Registered Agent, whether that be a third party or someone in your company, you or the third party can do that by filing a Change of Registered Agent filing with the state.
For example, Discern automatically changes your Registered Agent with the state upon sign up so that you don't have to.
Unfortunately, traditional Registered Agents rarely verify whether they are still your Registered Agent before sending you a bill, so you may receive a bill for Registered Agent services even after switching Registered Agent.
Typically, the simplest way to stop them from sending you invoices is to either email or call your old Registered Agent to let them know you’ve switched.