Is there a particular reason you want to stop taking them? If so, you will need to be sure you are getting enough proper nutrition from your food in their place. The reason most people take a vitamin is because they aren't sure their nutrition is OK without them. But you can get what you need from food if you pay attention to what's in the food and to what you need.
You could write down your standard breakfast, lunch and dinner and then look up the nutritional value of those foods. Then compare what you're eating to what you should have every day in terms of vitamins and minerals, and go from there.
If I were taking no other vitamins, I would take a B complex, C, D, and calcium, and most likely would take iron also. You could take them separately if you don't want to take a multi.
The following is from Wikipedia:
Hypervitaminosis or vitamin overdose refers to a condition of high storage levels of vitamins, which can lead to toxic symptoms. The medical names of the different conditions are derived from the vitamin involved: an excess of vitamin A, for example, is called hypervitaminosis A.
Generally, toxic levels of vitamins are achieved through high supplement intake and not from dietary sources. Toxicities of fat-soluble vitamins result also can be caused by a large intake of highly fortified foods, but foods rarely deliver dangerous levels of water-soluble vitamins.
The Dietary Reference Intake recommendations from the United States Department of Agriculture define a "tolerable upper intake level" for most vitamins.
High dosage vitamin A; high dosage, slow release vitamin B3; and very high dosage vitamin B6 alone (i.e. without vitamin B complex) are sometimes associated with vitamin side effects that usually rapidly cease with supplement reduction or cessation.
With few exceptions, like some vitamins from B complex, hypervitaminosis usually occurs more with fat-soluble vitamins, which are stored in the liver and fatty tissues of the body. These vitamins build up and remain for a longer time in the body than water soluble vitamins.
* Hypervitaminosis A
* Hypervitaminosis D
* Hypervitaminosis E
Vitamin C has a brief, pronounced laxative effect when taken in large amounts. This effect can be lessened by taking the large amount 5-10 grams per day in divided (smaller) doses.
Vitamin B6 excess can be mitigated by taking a low-dose B6 supplement together with a B-complex (which normally also contains B6), or with food rich in B vitamins, e.g., cereals.
High doses of mineral supplements can also lead to side effects and toxicity. Mineral-supplement poisoning does occur occasionally, most often due to excessive intake of iron-containing supplements.
If fear of hypervitaminosis is what is driving your decision, I would simply be certain that I am not taking excessive amounts of the fat-soluble vitamins or excessive amounts of iron. It does not sound like there is an absolute, i.e., if you are taking any multivitamin for more than two years it is inevitable to get hypervitaminosis, or anything like that. It also sounds like if that were your problem, you would know.
Anyway, good luck with your diet.