Hey there, @paul83.

Thanks for following up with us. I'm happy to provide the trial links for 2015-2018. No purchase would be required to use them. 

I've included the list of trial links below, along with their License and Product numbers. 

Desktop 2018 Premier Trial:

http://dlm2.download.intuit.com/akdlm/SBD/QuickBooks/2018/US_R1/QuickBooksPremier2018.exe

License number: 2242-9013-2805-438

Product number: 587-405

Desktop 2017 Premier Trial
http://http-download.intuit.com/http.intuit/Downloads/2017/Latest/Setup_QuickBooksPremier2017.exe
License number: 6488-2251-3382-188

Product code: 766-119

Desktop 2016 Premier Trial
http://dlm2.download.intuit.com/akdlm/SBD/QuickBooks/2016/US_R1/QuickBooksPremier2016.exe
License Number: 622444428497989
Product Number: 645812

Validation Code: 237135

Desktop 2015 Premier Trial:
http://dlm2.download.intuit.com/akdlm/SBD/QuickBooks/2015/Latest/QuickBooksPremierSub2015.exe
License: 648822513382188
Product Code: 518507
Validation Code: 317107

Just as my colleague suggested above, you'll want to ensure that you gradually upgrade your file. You'll upgrade using the trial links to make the final update in 2021. Please let me know if you have further questions or concerns about this process. I'm happy to lend a hand. Take care and have a wonderful day ahead!