You can update/change your registered mobile number with your Giottus account. Write an email to support@giottus.com from your registered email id and complete the following verification process.

1. Reason for changing the mobile number.
2. New Mobile number and current registered mobile number.
3. In a white paper write 3 details,
     o Giottus
     o Your registered email
     o Today date
4. Hold this white paper, your ID Card (Aadhar/Voter ID/Driving license/Passport/PAN card) and take a photo along with yourself. (Check this sample image for your reference).  

5.    Our team will contact you further to complete the process.