I saw that Pioneer was selling the 4.0 firmware for the x/f-series avic head units but cant seem to find any information on it anymore...... and I don't see any how-to guides on how to install it..... Any ideas why this is? Thx

No firmware updates, only pricey map updates available. Its unlikely that Pioneer will release any further updates as they have abandoned the f/X series hardware in favor of going the 110 route which can't be modified

The firmware of the latest map upgrades is labeled 4.0 but that means nothing in reference to new features or bug fixes. And as stated above, once a unit is discontinued there is no further support.