Going from T-Mobile D801 > AT&T D800

Hello all.

How do I go about going from a stock tmobile D801 firmware to AT&T D800 firmware? I tried using the LGFlashTool and it keeps giving me either a CrossDL D801 to D800 error. This is when I use the LGUP_8974.dll file and a LGD800AT-01-V10d-310-410-AUG-14-2013+0.tot. If use use the specific DLL for the D801, I then get a BIN Model is Different" error.

Thanks

Mark

lg g2 d800 ... i want to update to lollipop or marshmellow help meee !!!

hello devs
so i bought an lg g2 d800( at and t ) 32gb
now its android 4.4 and i want to update it
the problem is sim card ... its unlocked and i am unsing another phone carrier
i dont know anything about how to update so guide me goin through tall steps
and its rooted ... and will sim card stay working ?
thank you !