If the online reservation tool doesn't show an upgrade option for awards, then the hotel didn't load that. You can still call the hotel, ask for the manager and see if they might be willing to upgrade you to a CL room using award upgrades. They may or may not do that for you, but I do believe you best option is to call the hotel

Of course you might try the MR Silver reservation line and see if they will call the hotel on your behalf. As a Plat I will normally call the Plat line and they will call the hotel for me, but I don't know if the Silver elite line agents will do that or not.