change admin username account

hello.a few months ago my brother install win 10 to my laptop.i don't know which name choose but in user folder i see in
user folder in admin folder account the user name ''nikol''.yesterday i reinstall win 10 using media creation.i choose during installion a different name.but installation is finished i saw that the user name ''niko'' remain.i don't remember anything problem
like that in win 8-8.1.is a bug?can i rename user name of admin folder?

It sounds as if you did an in-place upgrade not a clean install. You can't rename the existing admin account but you can create a new admin account and then delete the user nikol. Alternatively you could again try to do a clean install and delete all partitions when you get to the screen asking where you want to install Windows.