You can renew your license from the avastUI and pay for another year. If you renew from the avastUI, then your new license would include the remaining time period left on your old license.
Regardless of wether I renew or not, I should not have to put up with nag screens in a product I have paid for. I know my licence is running out and I may renew but these constant advertisements in a product that I am still licenced for is really annoying.
You could always go with the likes of Norton who used to just debit your credit card again (I don’t know if that this their current practice) and not bother with the reminder.