At the moment we have a toilet downstairs and the bathroom upstairs. We are going to change the bathroom suite and would like to add a toilet upstairs, would this be much of a problem and should it only be done by a professional?
Virtually anything can be done at a cost, but the cost entirely depends on solving the technical side of where the soil pipe dumps to. You are going to have to ask another 'professional' who needs to assess the exact position of the layout and the existing pipework you have.
This work requires to be done in compliance of Building Regulations (Drainage 'rules')