If you access your box via SAMBA there will be a folder called upgrade - place the tar in there.
I am a little confused, in your opening comment you say you are running LE, so if that is the case then your upgrade that is causing problems is an LE upgrade (it could not be accessing the CE download links). So your problem is a with an LE upgrade and has nothing to do with CE. Am I reading your comments correctly ?
If you are running LE and trying to move to CE then the only recognised method is to run the CE as a fresh install off of an SD card. If you then want to load it onto your boxes NAND/eMMC then you can attempt the unsupported “installtointernal” which will give you a completely clean install of CE.
A bit of clarification seems in order.