Hi and Welcome to the forum, you might want to have a look at the following FAQ which explain where everything is
Welcome to Benefits and Work It could be argued that your care and mobility needs have not changed. That depends, partly, on what those needs are. To give a silly example - someone claiming they cannot walk for more than 20 meters who then gets a round as a postman would clearly need to notify DWP and explain how they are managing to carry out the job if their condition has not improved.
However, most cases are rather less black and white than this!
Our attitude is usually that it is better to notify DWP when it is not strictly necessary than be hauled over the coals, and possibly face a charge of fraud, later.
You need to be aware that any change of circumstances notification could trigger your move to PIP.