The Render Manager > (select a pass)
Set the current pass and choose Render > Render > Pass Options or Pass > Edit > Edit Current Pass from the Render toolbar.
Tab: Output [Properties Reference]
Options: Pass Frames
The Pass Frame settings allow you to specify which frames are rendered for each pass. You can specify any one of the following:
Choosing this options requires that you also define the Start and End frames, as well as the Step value (the increment between rendered frames. For example, a Step value of 4 means that every fourth frame is rendered.
Frame Set: renders a specified set of frames (1-100 for example).
Choosing this options requires that you also define the frame set to render, which you can do in the Set text box.
Timeline: renders all frames in the sequence as defined by the scene's timeline.
Use Scene Render Options: renders the frame range, set, or timeline specified for the scene render options. See Specifying Frames to Render.
You can also check the Skip Frames 
Skip Already Completed Frames box to skip frames that you already rendered.
