You can take either the Arlanda Express express train or Flygbussarna (the airport coaches).

The airport bus leaves every 10 mins and takes 40 minutes to the City terminal (the main bus station, next to the railway station).
The express train leaves every 15 minutes but takes only 20 mins, on the other hand it is twice as expensive as the airport bus.

Both the City terminal and the railway station are located within walking distance to Sheraton (less than 5 mins walk, basically just around the corner).
Both options are fine, which one you choose probably depends on your budget and how quickly you want to get to the hotel.