The ‘update’ install files you have (the downloaded zip file) do just that - they update an existing installation. This is more important for someone who has been using a previous version and has personalized their installation - i.e. made a lot of preference changes etc. but it makes no difference if you haven’t.
Point is, the majority of files have already been installed so you only need to install the update.
I believe one can choose the same folder as the original and then you will have a single installation. Alternatively you can remove the existing 7.0x installation after installing 7.5 with no problem.