How to make different numbers of ammos for different levels?

I think you should have a look at the basic of unreal first, cause storing variable and changing the value is one of the most common thing.

Here a introduction to blueprint:

So first theres no specific way of doing what you asking for, I can think about 3-4 way of doing this quickly. First way would be to simply increase by 10 the variable «ammos» store in your «Game Instance» object, which is a persistent object. That mean you can easily access this from any level OR blueprint.

Because I got the feeling you are really new to unreal, here a video that explain how to use «Game Instance».

Hope it help!

Example: I want to make a shooter game, which contains 50 or more level .so i want to make that my first person player is having 10 ammos in 1st level, 20 ammos in 2nd level …and so on., and i am using line trace by channel in my game.
please help me.

Thanks for help

I have a very beginner friendly tutorial series that will walk you through things like creating variables, casting, save/load, persistence between levels etc that you may find useful in addition to the above resources. As the above answer suggests there are many ways to do what you are asking.