Before you attempt to clean your grinder, disconnect your grinder from the power plug at the wall - it would be a disaster to have an accident. Remove the bean hopper from the main unit and give it a general clean using mild soapy water and a cloth. Remove the burr set or grinding wheel and give it all a good general clean using a stiff brush (a toothbrush is perfect). Be careful not to get the grinding wheel or burr set wet as it may be prone to rusting. Reassemble everything and check its operation.
Its a good idea to replace the burr set or grinding wheels every year or so, depending on the use it gets. For heavy duty commercial grinders, your grinding wheels can be resharpened professionally at less cost to replacing them - keep in mind that depending on the turn around time of the resharpening process, you may be without your main grinder.