I think there are two different Denali bikes. A flat bar Denali and a drop bar Denali.

If you have the drop bar Denali, usually there is a screw (often Allen type) behind the lever holding the lever to the bars.

Depending on the type of lever, some have a hole in front that you can fit your wrench through. Others, you open the lever to get the wrench in.

It may help to remove a wheel to better release cable tension, or open the cable tension release.