How do I upgrade Ubuntu 14.04 LTS to version 20.04 LTS? [duplicate]
In theory it might be possible to do-release-upgrade, but only stepwise via 16.04 and 18.04 to 20.04 (the LTS releases). It would take a lot of time is is very likely to fail somewhere.
I recommend that you backup your personal files (documents, pictures etc) to another drive) and after that make a fresh installation of 20.04.x LTS (it is at the third point release now, 20.04.3 LTS). It will probably be much faster and will give you a much cleaner system.