there are 3 ways to remove them - that I can think of anyway ...
1. squash them between finger and thumb and give your fish a treat (they love squashed snails)
2. Buy an assassin snail - this takes longer as it takes time for the assassin snail to eat all the pest snails.
3. put a piece of lettuce in the tank at bedtime. In the morning there will be snails on it. Take it out and throw it away. It's a process that takes a while but I guess it's more humane than option one.
My preferred way is option 1 as it's done and dusted in no time. Try soaking any future plants in warm salty water (rinse well before adding to your tank though) It is said that this kills any pest snails on the plants but I'm not 100% that it actually works