Yes you can.
We don't have an automatic way for you to upgrade, but you can send us an email on firstname.lastname@example.org containing your upgrade request and your Brizy account email.
We will get back with a payment link that will let you purchase the WaaS license by paying only the difference between your current license and the WaaS license.
Lifetime to WaaS upgrade
If you own a Brizy PRO Lifetime license and want to upgrade to a WaaS license keep in mind that you will benefit on the discount (provided by the cash you already paid on the Lifetime license) but you will lose the "lifetime" part in the process.
In other words if you want to keep your Lifetime license and also own a WaaS license, the WaaS needs to be a separate purchase