In order to lead or follow the toe-heel swivels, both man and lady must maintain a fair amount of tone in their connected arms. With sufficient tone through the connection, the man indicate which way he would like the lady to rotate through subtle impulses with his hands: One hand will give a push impulse while the other gives a pull impulse. The direction of the lady's rotation is determined by which hand pushes and which pulls.
Note that I use the word "impulse" to indicate that it is a brief action, not a sustained one. When the man wants to lead the lady to swivel in place, it is necessary to use the tone in the arms to brace the lady, so that her weight stays on her foot while swiveling. Most of the time his action can be described as "bracing" the lady, with the push/pull being only a quick impulse, such that the hands do not even visibly move.
The lady should remember that she, too, is responsible for maintaining tone. There is nothing the man can do to compensate for her lack of tone (although some men do still try, by pushing or forcing, which seldom works). His subtle impulses can only be felt when both partners have tone in their arms.
The upper-hand clasp is not essential, but very helpful to the lead. Just be careful not to use it as a way of "cheating" (eg When the man takes an upper hand clasp, it means toe-heel swivels). Whenever you use "cheating" methods for lead-and-follow, you ultimately end up cheating yourself.
I hope this helps!
Sincerely,
Jonathan Atkinson