The DR-1 service manual is on the free (with registration) Hifi Engine site, but it does not really tell you exactly how to change the pinch rollers. Other Nak service manuals with the same or similar transport may have better instructions.
My preference on these Nak decks is to completely remove the transport mechanism from the deck, and work on it with some wood blocks to prop it up. Then you can perform any required service or lubrication, and use your plate gauge or Nak alignment device to check alignment of the mechanism. I doubt it is possible to change the rollers without removing the mechanism.
You can certainly change the pinch rollers and ignore any check of the rest of the mechanism. You need a way to remove the small e-clips and small pliers to handle the spring and reattach the e-clip. The takeup roller is non-adjustable, but the supply roller may require a gauge and height adjustment IIRC. Speed fluctuation may also be a bad capstan belt or flywheel lubrication, so changing rollers may not be your solution.