You can move back and forth between keys by clicking the Previous Key and Next Key buttons 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 by turning on the 3ds Max Key Mode Toggle, selecting an element associated with a given track, and then using the 3ds Max buttons Next Frame and Previous Frame. 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 back and forth between keys in Key Mode.

You can delete a key by clicking Delete Key in 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.

Tip: When you've selected the biped part you want to transform, click Lock Selection Set 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 Lock Selection Set is the spacebar.