You can install FB, basta nakabind pa or meron history ng app installation.
Kaya no worries to install and no errors, but! Facebook and Messenger, running on lower version, syempre what do you expect on A4 Chip and instead. Install a Cydia Jalibreak using Pangu para manibago ka.
Actually, still usable naman ng iPhone 4 these days, basta tatandaan lang na meron history ng Apple ID sa installation.
If wala pa at bagong gawa, download ka lang ng older iTunes para makapagsync and makapagbind ng app sa Apple ID mo para mainstall siya sa iPhone 4 mo, without a hinch or errors, except sa Download on Older Version Pop-Up.
I hope understand this thing, if you need explaination. Go on Mr.Google to clarify more.
And to format you're phone, hold Home Button then connect sa PC.
Hanggang meron kang makita na, iTunes logo (kulay Blue) sa iPhone mo. Then open iTunes and click restore. Accept the terms and conditions and wait until it's done.
If namatay, just do it again and wait, until meron loading bar sa baba ng apple logo.
If meron error sa installation, press home button and power button (same time) for 10secs.
After mareached ng 10 sec mark, without letting go the home button, release the power button and continue hold the home button for 10secs, and restore mo ulit.