This simple script changes the first frame, last frame and frame step of the first render item in the scene. This is a bit easier than calling three separate item.channel commands and making sure that the first render item is actually selected.
The first and last frame arguments are required, while the frame step is optional. This sets the first frame to 1 and the last frame to 60.
This script could be simplified by directly selecting the render items with Select.itemType, but this extended version can be used as a framework for other scripts that operate on item types.