upgrading SQL Server 2017 Standard to 2019 Enterprise
you are asking two things.

edition upgrade
version upgrade

edition upgrade is when you want to change from standard to enterprise.
https://docs.microsoft.com/en-us/sql/database-engine/install-windows/upgrade-to-a-different-edition-of-sql-server-setup?view=sql-server-ver15
It is quite easy, mount the sql image and in the menu select maintenance then edition upgrade. Try it on your staging server and go easely.
Version upgrade is when you change sql server version from 2017 to 2019. This is something you have to test carefully because can generate performance regression in query plans or other issues in appplication activities.
MIcrosoft suggest to evaluate it using this model:
https://docs.microsoft.com/it-it/sql/database-engine/install-windows/choose-a-database-engine-upgrade-method?view=sql-server-ver15
I suggest you to upgrade on a new server as a side-to-side migration, starting from DMA:
https://docs.microsoft.com/it-it/sql/database-engine/install-windows/prepare-for-upgrade-by-running-data-migration-assistant?view=sql-server-ver15
Then do some test migration to a new sql server 2019 env end test deeply applications.
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly