Reducing the Clip Length—To trim the front of the selected clip, position the scrubber at the time you want the clip to begin, then press the W key or select Edit > Trim Front to Scrubber. This trims the clip up to the scrubber, thus changing the start time—but it does not alter the referenced media.
To trim the end of the clip, position the scrubber at the time where you want the clip to end, then press the E key or select Edit > Trim End to Scrubber. This trims the clip (not the media) after the scrubber.