You need to qualify for the demo first (pre-order the game, and are a member of EA Access or Origin Access). There will also be a public demo later, after the VIP demo.
The demo doesn't start until January 25, so I wouldn't expect to see it available to download until the 20th at the absolute earliest. Probably more likely to be 22nd or even 23rd.
My guess would be you will receive an email with a link to the store listing once it is available if you pre-ordered digitally, but I can't confirm that.
If you pre-order the physical edition, the retailer will need to provide you with a code to download it.
