.w .trx install

I've just bought a RT-AC68U and I'm trying to install the Merlin FW to get the most out of my router. When unzipping the download I get a file called RT-AC86U_382.1_0_cferom_ubi.w, which seems odd to me since the FW from Asus ends with .trx (FW_RT_AC68U_300438218881.trx) I can't load the...