Six at the top means:

The prince shoots at a hawk on a high wall.
He kills it. Everything serves to further.

The hawk on a high wall is the symbol of a powerful inferior in a high position who is hindering the deliverance. He withstands the force of inner influences, because he is hardened in his wickedness. He must be forcibly removed, and this requires appropriate means.
Confucius says about this line:
The hawk is the object of the hunt; bow and arrow are the tools and means. The marksman is man (who must make proper use of the means to his end). The superior man contains the means in his own person. He bides his time and then acts. Why then should not everything go well? He acts and is free. Therefore all he has to do is to go forth, and he takes his quarry. This is how a man fares who acts after he has made ready the means.