If there's 1st class availability, which is possible on DTW-JFK depending on days/flights, the cost would likely be $50. You'd only be offered this at the airport... you wouldn't be able to call to secure the upgrade.

The $50 would buy you:
- Early boarding
- Quick deplaning
- About 4 more inches of pitch and 2.5" of width
- Guaranteed window or aisle
- Complimentary alcohol and probably a salty snack in a shiny package
- Pre-board beverage (most likely, depending on time)
- Use of the 1st class lavatory
- Personalized service from the 1st class FA
- Less competition for overhead bin space
- That "feel good" feeling of avoiding the riff-raff in coach

For a short DTW-JFK flight, you'd need to decide if it's worth it for you.
If you've never flown in 1st before, and $50 isn't an issue, then heck, go for it (just keep your expectations relatively low).