Go to Settings > Security and toggle on Unknown Sources . This allows you to install apps from outside the Play Store.
While your device won't stop working immediately, it will no longer receive updates, security patches, or the ability to run many modern apps from the official Play Store. How to Manually Find the APK download google play services apk android 4.4.2
Before attempting to install, it is important to understand the technical constraints of Android 4.4.2: Go to Settings > Security and toggle on Unknown Sources