I used an ordinary mobile phone for a good while. It was OK for phone calls and not much else. Not at all smart by today's standards. The one I have now has got all the bells a whistles of a fairly modern smart phone. One trouble about not having a smartphone is that some banks and shopping sites want to send a log in code by text as a security measure. Oh well, progress I suppose.
About the computer, If you don't have any files that need rescuing (because you have them backed up to an external drive), it might be best to just clean install the operating system and programs and put your files back on afterwards. This will give a nice clean system.
This is done with the W.10 installation media mentioned in the last post. Boot up with it and follow the instructions. If you have a Microsoft account, all you need is the the login details. If Windows 10 has been installed before, the Microsoft servers know this and no key number necessary. You'd need to have key numbers for the programs you want to install on the OS though.