See the attachment for an overview of removing the main fan from a dryer.
Most dryers use a similar design tapered shaft and hub for the main blower (fan).
Penetrating oil may help the process of loosening the hub to shaft fit. A steel bar puller with bolts mentioned will help the process.
Loosen the locknut but do not remove it to help contain the fan from falling after breaking free of the shaft.
Helpful Tip: Instead of using a hammer and cold chisel, alternatively you could buy a spanner socket. See images below.
Thanks, John, for teaching us that the right tool goes a long way.
Note: See this article if you need new blower bearings. 
