If you're taking the Greenway north, yes, there's a set of stairs that you have go down just south of Dyckman. The steps are long and shallow. There are ground level "banisters" on either side, and it's possible to put your bike on them and roll down. This puts you on Riverside, then Staff St., which leads to Dyckman. Be aware, they're repaving Dyckman, so as of right now, the street is milled, and really unpleasant to ride on.

How will you continue north? Will you take the Henry Hudson Bridge? If you want to continue along the river, you can turn left on Dyckman, continue to the end, where you then enter Inwood Park. However, you then have to cross railroad tracks, which means using an footbridge and climbling a real set of stairs. It has one of those rails on the steps for bike tires, but it's steep, and quite a push.

You can avoid the overpass by turning right on Dyckman, and take Seaman north (that intersection is a bit of a mess), and enter the park at 218th St. Either way, once in the park you have to go up a very steep hill, and finding the entrance to the pedestrian path on the bridge is tricky the first time you try. Since you're in a park, you're on paths with no names and no signage, so it's hard to figure out where you are.

Anyway, I hope this helps.