Open Gmail > Click on Can't access your account? > Select I don't know my password > Enter your E-Mail ID and click on Continue button > Enter the Captcha as shown in the image and click on Continue button > When Reset your password using the verification method below: appears, click on hyperlink.
Verify your identity from the line Can't access any of these recovery options?
Verify your identity by answering multiple questions about your account.
Follow the onscreen instructions by providing correct information about your account.
You can also follow the instructions on this link.