As referred in the WhatsApp FAQ:

You can transfer chats from one Android phone to another. To do so, please follow these steps:

1. To start, make a backup of your most recent chats.

   • Go to WhatsApp → Menu Button → Settings → Chat settings → Back up chats.

2. Next, transfer this backup to your new Android phone.

   • If your phone has an external microSD card, take the microSD card out of your old phone, and pop it into your new one.
   • For phones that have an internal memory / internal SD card (like most Samsung devices), you will need to transfer the /sdcard/WhatsApp/ folder from your old phone to the same folder of your new phone. There are a couple of ways you can do this. You can use a file explorer or even transfer the backup files to your computer.
   • Please note that it is possible to be missing some files during the transfer. Please double check to make sure all the files you wish to transfer over to your new phone are included in the backup.
   • If you are unsure about what kind of SD card you have, we recommend checking your phone's specifications on your phone manufacturer’s website.

3. Once you have safely transferred your backup, you can install WhatsApp on your new Android phone.

4. During the installation process, WhatsApp will automatically find your backup and ask you if you would like to restore it. Once restored, your old chats will appear on your new phone.