i want to do my own oil change, so i bought the 10w30 synthetic oil.

i remember asking the guy how many quarts/litres i need, but i forgot. i bought more than enough, so im not sure how much i need.

10W30 is not an approved weight. You should be using a MB lubrication specification 229.5 oil (that approval code will be noted on the back of the bottles) for your vehicle. Depending on the manufacturer, it's either a 0W40, 5W30 or 5W40 oil. No 10W oil is approved.