can I upgrade my 2019 desktop license to 2020 and how much is it?
You can upgrade. Start here: https://www.sketchup.com/license/renew
If your Maintenance and Support is current it may not cost you anything.
I have reason to think that your support was due to renew on May 15th last year. When you go past 30 days of that date there is a $60 reinstatement fee. That fee doesn’t increase until you go past one year overdue. The 12 months M&S itself is $120, so with the $60 reinstatement fee you would pay $180 to get up to date, and that would include all updates for the next 12 months. That is pretty certainly going to include SketchUp 2021, you would not have to pay to get that version if you get up to date now.
If I’m right about the date, and you don’t get around to this until May 15th or later, the reinstatement fee will have gone up to $120.
How do I renew my license
Did you try the link I provided earlier?
missed it. Thanks