How do I get rid of them?
Some ant species are considered pests, and because of the adaptive nature of ant colonies, eliminating the entire colony is nearly impossible. Pest management is therefore a matter of controlling local populations, instead of eliminating an entire colony, and most attempts at control are temporary solutions.
The cheapest, but not necessarily most successful, way of dealing with an ants nest is to pour boiling water onto the nest. This will certainly control the problem, but may only be a temporary solution. Another way of eliminating an ants nest is to buy a household insecticide which you should apply on and around the nest, together with possible entry points for the ants.
Both the methods described above are worth a try, but if you still find you have an infestation we would recommend you seek professional help.