The KATANA-50 MkII EX has 4 Channels available from the top panel.
BANK A: CH1 and CH2
BANK B: CH1 and CH2
However, the KATANA-50 MkII EX, has 8 Channels accessible if it's used with the BOSS TONE STUDIO for KATANA Mk II (Windows, macOS), or with either or both, the GA-FC/GA-FC EX proprietary footswitches.
The BOSS TONE STUDIO software editor and the GA-FC/GA-FC EX allow for full access to all 8 Channels.
BANK A: CH1-CH4
BANK B: CH1-CH4
See "Using BOSS TONE STUDIO for KATANA Mk II" for details on the setting procedures.