How to make superuser from non superuser in PostgreSQL

[Sunil Jadhav <sunilbjpatil@xxxxxxxxx>]

Hello Team,

I have login with non super user in PostgreSQL instance.

How to become a super user

I tried and getting a below error 

 "must be  superuser to alter superuser" 

 How to resolve this?

I don't know the superuser password?

Thanks for your help in advance

Thanks

Sunil jadhav