Kaspersky Internet Security for Android has the following activation options:

• Free version is automatically activated after the app is installed, if you have not entered an activation code for Premium version. The free version includes the Scanner, Anti-Theft, and Call & Text Filter features and has no time limitations.
• Trial version allows to use all the features for the 31-days period. The trial version can be activated at any time after the installation, if it was not used earlier or is not being used at the moment. Upon expiration of the trial period, you can buy an activation code for Premium version or return to the free version.
• Premium version grants access to all the application features for one year. To activate the Premium version, use a 20-digit activation code. Your device must be connected to the Internet to activate the product.

For the guide on activation, see the article How to activate Kaspersky Internet Security for Android.

An unused activation code can be activated at any time, but the license will begin to expire on the day of initial activation. The license term is counted starting from the moment of activation. 

If you have a valid activation code for Kaspersky Tablet Security (Android OS) or Kaspersky Mobile Security (Android), you can use it for activating Kaspersky Internet Security for Android. If you have an expired activation code, use it to renew the license at discount.

To check your license expiration date:

1. On the main screen of the app, expand the quick access panel and tap Settings.

2. Tap Additional.
3. The Licensing section contains the information about license expiration date and remaining days.

Once the Premium version license expires (one year after the moment of initial activation), the application will automatically switch to the free version.

To continue using the Premium version, buy a new license and activate the application with the received activation code. You can buy the new license in the online store or in Google Play.

To renew the license, you do not need to reinstall the app.