Advice on upgrading firmware on Ledger Nano
1st test your 24 word recovery backup with Electrum . Electrum as Ledger using BIP39 seeds. Crate new wallet with Electrum and choose " I already have a seed" then enter the 24 word recovery backup. 

You can do it from Tails live system if you worried of keyloggers. No need to  connect to internet if you don't need to see your balance but just want to test your seed.