Are you on a Mac or a PC? If you are on a PC, just follow the following steps:
- Go to Control Panel. --> Click "Change keyboards or other input methods"
- Select "Change keyboards" --> Click "Add" and scroll down to find Japanese and check mark the first two (Japanese & Microsoft IME) in "Keyboard" and the only one (Ink Correction (64 bit only)) in "Other".
- Go to Language Bar and make sure you select "Docked in the taskbar" since it makes it easier to switch between the kana.
- Go to Advanced Key Settings and find out which hotkeys you need to press to switch between the input languages. I think the default is Left alt + shift.
That should do it. Make sure you select English as the main input language so it doesn't cause you problems. Let me know if you have any further questions.