If you're switching between Android phones, backup your Whatsapp chat history on your old phone to Google Drive, then install Whatsapp on your new phone and follow the instructions.
Wechat is simpler, I think you just need to scan the Wechat QR code on your old phone with the new phone's camera.
If you don't install a lot of apps, don't have text notes and don't have a super huge list of contacts, you can just manually type in the contacts on your new phone.
There are guides online to refer to.