Step 1: Select the backup file you want to restore and rename it from msgstore-YYYY-MM-DD.1.db.crypt14 to msgstore.db.crypt14.Step 2: Uninstall the WhatsApp app from your phone.Step 3: Go to the Google Play Store and download the new version of the app....
On Android, either get this file: /sdcard/WhatsApp/Databases/msgstore.db.crypt (crypted database on SD card, can be created by starting backup from whatsapp advanced settings: settings - more - Backup Chats) or these files: /data/data/com.whatsapp/databases/msgstore....