Don't mix right away. You'll need to introduce one food at a time, and slowly. So choose one food, give your hedgie a week or two to settle in and eat the same food as the breeder was feeding (so make sure you get a month or so's worth of food from your breeder, or buy a small bag of the food they feed), then slowly add in the new food. The usual schedule is 1/4 new to 3/4 old for week 1, 1/2 and 1/2 for week 2, 3/4 new to 1/4 old the third week, and then all new. Then after hedgie's switched over and doing well on the first new one, you start adding in the second food in a similar manner, until they're mixed at the ratio you want (such as 1/2 and 1/2).
After that, it's up to you. I always just counted out the same number of kibble for each of Lily's foods each night. Other people do just mix both bags up all together and store them that way. Either way works!