Can I purchase upgrade since I have a license for previous version?

Yes. You may purchase upgrade to get the latest version of Foxit PDF Editor 11.x from the link below.

https://www.foxit.com/shopping/upgrade.html

Currently Foxit online upgrade system only supports customers who purchased the upgrade from PhantomPDF 9.x and 10.x. For customers who purchased earlier version before 9.0 like 8.0, please visit Foxit online store to order a new license.