I only know how to do this on Windows (but it should be similar on any OS, you will just need to find the correct location yourself – google search would help with that).
On Windows:
Go to your User Folder – on Windows 7/8 this would be:
[SYSDRIVE]:\Users\[your username] (ex. C:\Users\JohnDoe\)
In this folder there should be a folder called .AndroidStudioBeta or .AndroidStudio (notice the period at the start – so on some OSes it would be hidden).
Update
Now, Android Studio settings is at:
C:\Users\<Your User>\AppData\Roaming\Google\.AndroidStudio4.X
Delete this folder (or better yet, move it to a backup location – so you can return it if something goes wrong).
This should reset your Android Studio settings to default.