i replaced mine on the weekend as the bearing was starting to get too noisy to ignore any more. The big bolt MM is referring to is a 10 mm allen key. I was able to get a square drive allen key on a ratchet and crack it with a breaker bar. you dont need to remove any other bolts to remove the tensioner.
the only other bolt i thought you might be referring to is this one
http://uploads.tapatalk-cdn.com/2017...18ab43e83a.jpg
it looks like it might be a tamper proof head, you would be able to remove it with something like this
https://www.kincrome.com.au/torx-set-tamperproof-8-pce