FlyingFinn explains the process far better than I could.
AY should be able to check you in all the way through, HEL-MAN-ORD is actualy a very popular connection. If not, then there are transfer desks and they should be able to help you out.
The connection is a little tight, but perfectly achievable assuming the AY flight is ontime. Like also mentioned, if it all goes tits up the reroute via LHR is the fallback option, but with the inconvenience that the C upgrade probably won't stick.