It is not at all like Marriott here for upgrades. In fact I almost never get upgraded at Holiday Inns and only rarely at Cowne Plazas. When it does happen the room is usually assigned before arrival, so asking at checkin like you're supposed to will yield very low success. (I think my actual success rate when asking for an upgrade at checkin is about 0%)

But it seems that some others here regularly email the manager beforehand and have much better success at upgrades. I usually forget and then get annoyed that they say no when I ask at the desk. So you might want to try emailing ahead and politely asking for what you want, such as a club level floor or a junior suite.