There are a few different ways to move among biped keys and edit them.
You can move back and forth between keys by clicking 
(Previous Key) and 
(Next Key) on the Key Info rollout. The fields to the right of these buttons indicate the key number and frame number.
As with other 3ds Max objects, you can also move back and forth between keys using the general animation controls: Turn on 
(Key Mode Toggle), select an element associated with a given track, and then click 
(Previous Key) and 
(Next Key). For example, you can view keys, move between them, and set keys for a right arm track if any of the right arm's objects (clavicle, upper arm, lower arm, hand, fingers) are selected. Or use the < and > keys on the keyboard to move between keys in Key Mode.
To delete a key, click 
(Delete Key) on the Key Info rollout. The biped part that has the key must be selected, and the current frame must be the keyframe you want to delete. Keys that are locked (appearing in red in Track View) cannot be deleted.
(Selection Lock Toggle) on the 3ds Max prompt line. Now you can transform the part without accidentally selecting a different part of the biped. The default keyboard shortcut for Selection Lock Toggle is spacebar.