Cant log in to CMS

I am new with episerver but I am building a e-commerce site with CMS and Commerce and I have trouble to login at my CMS as admin. I have tried to change in my web.config file 

<location path="EPiServer/CMS/admin">
<system.web>
<authorization>
<allow roles="WebAdmins, Administrators" />
<allow users="*" />
</authorization>
</system.web>
</location>

But I still have to login and no username or password I have used works. Would apreciate some help please.