Where to find new firmware

For?  Most phones have a place in the Settings to check for updates.  Updates for most tech are staggered, which means someone else might get it before it is available to you.  That is done to prevent potential bugs from plaguing an entire line of a device.  Some devices allow you to update locally through a file on the internal storage.  This greatly varies by manufacturer and model.  What you are trying to update or find firmware for helps a lot in trying to figure out what the latest firmware is.