Open WhatsApp
Tap the three dots or Settings
Go to Linked Devices if you want to sign out from a connected device
Select the device
Tap Log out
On iPhone, go to Settings, then Linked Devices, select the device, and tap Log Out
To sign out from your phone, back up your chats if needed
Delete the WhatsApp app from your device
If using Android, go to Settings, Apps, WhatsApp, then Uninstall
If using iPhone, press and hold WhatsApp, then tap Remove App
To stop using your account completely, delete your WhatsApp account from Settings, Account, Delete My Account