Below command will display both max receive and max send size
get-transportconfig | fl M*ze

Below command will display max receive size
get-ReceiveConnector | ft Id*,M*ze

Below command will display max send size
Get-SendConnector | ft Id*, M*ze

To Alter the limit, the commands are below, but would recommend you change this via the Exchange Management console if you have SP1 and above installed

This will change the receive limit. Input figure as required.
Set-ReceiveConnector ” ” -MaxMessageSize MB

This will change the send limit. Input figure as required.
Set-SendConnector ” ” -MaxMessageSize MB