Modifing default amount of text for a post on the home page

Is there a way to allow more text of a post on the home page to show than the default that the Montezuma theme allows? Please see my screenshot for an example.

Ideally, I'd like to just have the front page show as much of any given post as I want, until I insert the "more" tag. I haven't been able to figure out a way to do so, so the theme just ends up cutting off the front page excerpt at some default value.

Thanks in advance for your help!