There is a very easy way to do this. You will require another device which is a newer one. What you have to do is:
1. sign in to your Apple ID with the other newer device.
2. Download Facebook messanger with that new device.
3. Delete it from that device. Now the app will be in your cloud.
4. On your iPhone 4 search for ace book messenger.
5. Click download and it will ask you if you want to download an older version of this app. Click download and wait for it to finish!!
6. Hope this helps! This work with all other apps that will have an older version of it