You can change the display name that people see in Gmail by changing your Google profile name at the Google About Me web page. Select the pencil in the upper right corner to edit your Gmail display name. This will only change your display name, and will not affect your account name or actual email address.
If you would like to change your preferred first name in other university resources, please contact either the Registrar's office or Human Resources. More information is at The Registrar's Preferred Name web page.