Question on 780 mini tower with windows 10 Pro

I bought a refurbished Dell OptiPlex 780 mini tower. It came with windows10 Pro installed . I am not very experienced with windows 10 I just am now a bit familiar . 

The issue is when they installed the windows OS they made their own administrator and I want to make it my own name . It's not a windows log in but a local login . 

 Does anyone know how I would do this. From what I understand go to control panel and you can change the name and I'm not sure if I can make a password . 

 I got this Dell tower refurb because of the funds I have and it works great . My last tower was an Acer M261 running XP Pro and it still works . In 2009 the old monitor died is was not a wide screen so someone set me a video card and I installed it and the drivers . The Dell has it's own built in video on the mother board and didn't offer my 1366 x 768 that is the only one my Dell IN1910N flat screen supports yet through my trying some how windows 10 Pro found a driver that works it's a forced PNP . I could probably use the video card from the Acer and then find the driver for windows 10 which is probably different than XP , not sure. Yet the windows driver seems to work well . 

I used to be on this forum yet this year changed IP so my old email no longer works to log in.  

 my name is William I hope someone can help .