What is the best way to upgrade Debian Jessie?

[Linux for blind general discussion]

I don't know about downloading a new sources.list, but you could try
updating it manually.

Simply run:

sudo nano /etc/apt/sources.list

replacing nano with your editor of choice. and changing every instance
of jessie in the file with stretch. Or with stable if you want to
upgrade to buster automatically when it releases, though some might
consider that riskier than manually changing the release with each new
stable.