You can find your the area for editing your meta tags for your page as follows:
When you are editing a page of your site, click Page > Metadata to see the various fields for adding meta tags. For more detailed information on adding/editing these tags please see this link: Adding title, description and keywords tags.
You can also edit the Google Webmaster meta tag by going to Settings > Tracking. For more information here is a link to our tutorial: Verifying your site with Google Webmaster and submitting a sitemap.