The formal firmware updates are available only through OTA. However, it's undocumented how you can get the OTA downloaded files to use for manual updates.
I can say for Android as my phone is Android. When there are updates downloaded and pending to be pushed to the cam, the files temporarily exist in the hidden folder /Android/data/xxx.yyy/OTA/ (I forgot what exactly is the xxx.yyy). You can only open it and copy it from the computer your phone is plugged into. The files are with .bin or .zip extensions. Don't try to unzip it. Just copy it iver the the cam's (or sdcard) root folder...