Select the track you wish to edit by clicking its name on the left-hand side of the screen. Convert this track into a polyphonic track. You can do this quickly by clicking the empty gray box near the ticks and samples button located below the box containing the name of your track and selecting "Polyphonic."
Select the "Zoomer" tool, which looks like a magnifying glass and is located in the upper left-hand corner of the screen, immediately to the left of the "Trimmer" tool. Zoom in until you can distinctly see the fluctuations of the syllables of the word that you will be editing in the waveform.
Choose the "Selector" tool in the upper left-hand corner of the screen, located between the "Trimmer" and "Grabber" tools. Left-click with the "Selector" tool exactly where you wish to start lengthening your vowel sound, and your selector will mark that spot. Right-click and select "Separate" when the menu appears. Repeat this process once more at the exact location you your vowel sound ends. This will cause the vowel to be isolated as its own editable unit.
Convert your track from "Waveform" to "Warp" mode. The box for this is located between your track's "Name" box and the "Polyphonic" box and will show "Waveform" on its default setting. You can change its mode simply by clicking on it and selecting your desired view of the track.
Slide the surrounding parts of the word away from both ends of the vowel in order to make room for lengthening. This can be done by first selecting the "Grabber" tool, which is immediately to the right of the "Selector" tool and allows you to move any "Grabbed" section of audio, and then clicking and dragging your separated parts to a new location.
Right-click on the "Trimmer" tool, which is between the "Zoomer" and "Selector" tools. Choose the "TCE," or "Time Compression-Expansion," trimmer when the menu appears. This will change your trimmer's function. Instead of erasing and re-adding parts of your track every time you click and drag your mouse, your trimmer will now stretch or compress the entire selection without adding or deleting any edited material.
Move your mouse so that the trimmer rests over the edge of one side of your vowel sound. Click and drag your vowel to any desired length.
Return your track mode to "Waveform" and your trimmer to its original setting if you are done editing for word and vowel length. If you wish to edit other words, only return the track mode to "Waveform" so you can repeat the separation process.