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3. Military neutral: proxy forces and psychological warfare
When the military is not that interested, the US tries to turn them against the leader, corner him. They can (and do) use any policy instruments, everything short of US ground combat troops. Deny economic help, starting propaganda campaign (in the client country, at home in the US, or anywhere else), isolate the states from other countries, organize a proxy force, use bombing raids to help said proxy force. And then they do a demo of strength, send some ships with troops on deck and imply that they'll invade the country. At this point the leader resigns. Guatemala 1954, unfortunate Jacob Arbenz got on the shitlist of the United Fruit Company by enacting agrarian reforms.
4. Military opposed: coups d'état
Ah, qudetah. The optimum for the US. When the military wants the leader gone, the same person whomster the US wants to go. Nothing to do, just contact the military to do something, or encourage them, sometimes it's the military's idea to begin with. The US can give aid of course, send more arms or other materiel. But the main thing in this case to acknowledge the next leader who comes to power via the coup. Give him legitimacy. Usually the new leader(s) goes on giving a bit of arse licking to the US, to let the US know they are still the faithful servants of theirs.
Brazil, 1964, against Goulart. US sent help by ship, but the coup won just in a couple of days way before it could have arrived. Also Allende's mysterious suicide.