Hi,
In case you renewed your license you can try to unlink your license and then link it again. You can do this in Acymailing->Configuration->License.
In case your license was expired and you have purchased a new license you might have got a different license key. In that case you need to unlink you license and then link the new license key again.
You can find your licence keys on the license tab in your account on our main website.
