1. Sign into Google Webmaster tools at Google.com/webmasters.
Once signed in you'll see your site, or a list of websites that have been verified using Google Webmaster Tools.
2. Click the Manage Site Button and Choose Add or remove Users.
A list of Users and Site Owners will appear. There are two types of users that you can add to your Google Webmaster Tools account: Restricted and Full.
Site owners always have complete control over all settings in Webmaster Tools. A Full user can change most settings and take most site actions like submitting a new URL to Google's search index. Restricted users in Google Webmaster Tools are generally restricted to view only permissions.
3. Click Add a New User
Be Careful of who you give full access to. Google Webmaster Tools are powerful and can have a significant impact on improving or ruining your Website's performance.
4. Enter the User's Email, Select the Permission level and click Add.