If you already have good relations with them and your job is in a crucial non-expendable role, i'd give them a month. otherwise 2-weeks is fine.
a basic sentence would be something like this: "I would like to inform you of my decision to resign after ..... date in order to attend XXX School of Medicine."
now if you liked working there a lot, say something such as,
"It's been truly a pleasure working XY corp, I've learned an amazing amount of skills and have had some important formative experiences."
you might even add a few quick lines of personal examples of how you've grown or what you felt were your important accomplishments at the helm.
If there is some transfer of skills or ideas (like you work in biotech or in a laboratory), you can say, "My time in medical school will allow me to compliment my training under your organization..." and/or "I look forward to having a relationship with XY corp, albeit in a different capacity, in the years ahead. Respectfully yours, Jo Schmo"
or something like that~!
no need to burn bridges... something fruitful might come up in the future, you never know...
😉