SQL Server Management Studio Change User Server Roles to sysadmin?
You've explained that you don't have the SA password and you're not an administrator. In that case, you're going to have to hack your way around it.

See Think Your Windows Administrators Don’t Have Access to SQL Server 2008 by Default? Think Again. by Argenis Fernandez.

That post explains how to impersonate the NT AUTHORITY\SYSTEM login using PsExec (or creating a Windows Scheduled Task running under the SYSTEM account) to create a new login for yourself. Then, you can log in via that new login, and grant your Windows account SA permissions.