You're unable to dismiss (or recall) the totems until level 30 when you can learn
Totemic Recall from a Shaman Trainer. This spell returns all of your totems that are currently in use and gives you back 25% of the mana used to cast them.
Before level 30, you destroy one totem by either running out of range of your summoned totem or by summoning another of the same type. An earth will replace an earth but not a water. For instance, a Stoneskin Totem would replace (and destroy) an Earthbind Totem because they are both earth totems, but not a Healing Stream Totem because it's a water totem.
This means you have to plan ahead and try to have "situational awareness". If your totem
could aggro a mob, then plan on attacking that mob, too. If you don't want to have to fight that mob, then try to place it in a different location so you can be more selective about who you might have to fight. (And watch out for patrols, especially in instances.
)