how to create database with in the sqlserver some error

Question

Cannot create file 'C:\Program Files\Microsoft SQL Server\MSSQL11.MSSQLSERVER\MSSQL\DATA\mydatabase.mdf' because it already exists. Change the file path or the file name, and retry the operation.

Msg 1802, Level 16, State 4, Line 1

CREATE DATABASE failed. Some file names listed could not be created. Check related errors.

how to solution for the above problem