Open the Dr.Web application; go to Menu (the three dots in the upper-right corner of the screen) → License → Enter new serial number. Enter your serial number, and tap "Activate".
No additional actions, including reinstallation, are required. The same method is suitable for activating a serial number when you purchase/renew Security Space that includes a free mobile version.
Activation error
If any error messages appear, try to activate your license using a different network connection.
If you continue to encounter problems, detailed diagnostics are required. Send a written request to our technical support service. Please attach the error screenshot to your request, and enter your serial number.