Sudden drop of battery life

Hello, I am a new owner of a Macbook Air.

For the past couple months everything has been working fine and the battery on my laptop lasted for at least 10h, but last week I noticed that the battery life isn't as long. Right now when the battery is fully charged I have only 4h of power.

I don't know why the sudden change, since I haven't done anything differently. Maybe I'm doing something wrong without realising. Anyway I would like to ask for some advice or ideas to help me solve this problem ( if it can be solved).

I really appreciate your help!