1. A printing apparatus comprising: a printing unit; a setting unit configured to set a printing condition; an inputting unit configured to input image data; a first controlling unit configured to control said printing unit to execute first trial printing according to the image data input by said inputting unit and the printing condition set by said setting unit; a first accepting unit configured to accept, after the first trial printing, a changing instruction for changing the printing condition set by said setting unit; a second accepting unit configured to accept, after the first trial printing, an execution instruction for executing a second trial printing; and a second controlling unit configured to control, in a case where said second accepting unit accepts the execution instruction, said printing unit to execute the second trial printing according to the image data input by said inputting unit and the printing condition changed in response to the changing instruction, wherein, in a case where said first accepting unit does not accept the changing instruction, said second accepting unit cannot accept the executing instruction.