The seven heads stand for the seven successive world kingdoms.

In Revelation 12:3, the crowns were on the heads.
....Here Satan is seen in his position through the past ages.

In Revelation 13:1, the crowns are upon the horns.
....Here Satan rules at the end of time, during the seventh kingdom.
....This is the kingdom of the Antichrist.
....The ten kings have come into power with the Beast.
....That is why the crowns are on the ten horns.