Put on your belt where the pots go and just press the number for it
Beware this can act in a way most people don't expect if you have multiple of them in your bag. For example, if you are wearing amulet and have poison on belt and press the number button for poison, it will jump into where the amulet is. If there's no poison in your bag, then the amulet will take its place on the belt, so they are effectively swapped. But if you have other poison in your bag then it will jump into your belt instead of the amulet, which is kinda annoying.
If your hunt requires you to take more than one of each with you, then your best bet is just having your bag open and right clicking on the thing you want to wear.
If that's too much work and you just want to play relaxed, then wear both at the same time, but it does waste a bracelet slot which isn't ideal if you're killing stuff that is hard for you and you need all the stats you can get.
It's not like this forever though, at level 180 you can wear special amulet that act as poison too, so swapping becomes a thing of the past!