Unfortunately we do not have a removal tool but we will be working on a tool very soon to remove 3rd party software, the problem is that typically it's best to use their tool due to the amount of hidden files that can be installed on the OS. So it's best practice, to remove the AV with their uninstall tool then install the Avast client since there will be issues when installing if remnants of the previous AV is still there.
I hope this resolves your issue but if you have any other questions please feel free to post again.
Kind Regards,
Che'