Running Database Script Error SQL Server/ Report Server

I keep receiving this error and am unable to fix it - can anyone help?

• Before I start the below instructions, I set up SQL Server 2014 on my computer.

What I did before?

• I change Use built-in account to Network Service;

• Then in Web Service URL section, I changed default IP-ADRESS setting All Assigned(recommended) into protocol form, and also
  TCP Port --> 80 to 800;

• After that, I came to Database section. I clicked on Change Database button --> Create a new report server database.

At the end of creating process I receive this error message:

Can anyone help me, please?

Your database user must be a member of dbcreator server role to create the ReportServer and ReportServerTemp databases.

To add a member to dbcreator, you must be a member of that role, or be a member of the sysadmin.

With the following script you can add permission required:

ALTER SERVER ROLE dbcreator ADD MEMBER YourDatabaseUser;