Start by watching some movies about veganism or reading some websites or books so you know for sure you are on the right path. We can give reccomendations if needed.
Start with just food (which causes the most suffering and affects the most animals) and I would argue meat, fish and eggs are the cruelest and most destructive foods so cut those out first. Later on you can consider cutting out cheese, butter and other non-vegan foods, and going beyond food to consider clothes, toiletries etc.
Replace meat partially with legumes (soy, lentils, peas or beans) and partly by eating more fruit, vegetables, and grains (bread, rice, pasta etc) which are good for you anyway and make up a good balanced diet!
Vegan diets can be low on vitamin B12, iodine, calcium, and omega 3s. For Vitamin B12 take a supplement, for iodine google the sources of iodine and eat some foods in the list that you like, for calcium a balanced diet including e.g oranges, green veg and some almonds is good for this. For omega 3s eat walnuts and/or ground chia or flax seeds. Most of all other things are taken care if you eat a balanced diet. None of this needs to be worried about in the first days, but just in the first weeks or months make sure you get a B12 supplement at least.
Get a vegan recipe book or look at sites online for some good ideas. If the food you are eating is boring get some new ideas, it shouldn't be.
You may need to eat more vegan food to fill up. Either eat bigger portions, extra snacks or one extra meal per day.
Understand that periods of transition from any one diet to any other sometimes (not always) produce changes/difficulties to the body. Give things time to adjust, but post here if you get any difficulties and sometimes we might be able to help.
You are on the right path and best of luck!
Are you living with parents and do you cook for yourself?