If it's so, then You can use this method. If Windows won't activate automatically after You have did everything as bellow said, tell me, I'll try to help You with Your problems.
Windows 10 home: how to upgrade to Windows 10 Pro?
It's simple. Turn off internet connection, open settings and go to Update & Security => then on right panel find Activation and click on it.
New pop-up window must open and there You can change activation key.
Insert this key:
and click Next etc. Follow instructions and then only wait untill everything ends.
It will take not long, then restart computer and after that can tunr on internet, if it doesn't turn on automatically after reboot.
So, now it has been done. Only one thing, it is activation. If Your computer was activated before with key ie You used Retail key or this computer was upgraded as OEM computer and had HWID (Hardware Identification) then it should activate automatically after some time. Sometimes You must login to You Microsoft account.
Did You mean cash?
You don't need any cash. Generally and usually you can do this update/upgrade for free. So far, I have not met anyone who should have paid for it.
Maybe You want to say what computer it is and if it came from store as new pc with Windows 10 already preinstalled, then shouldn't be any problems. I bought some months ago new Dell with preinstalled Windows 10 Home and did the same, couple days ago one user from another forum asked for help and I recommended this method, after 20 minutes he said, everything went well and Windows 10 Pro is now activated.
I cannot imagine any reason why You shouldn't get done in the same way.
I'm sorry, I really don't understand anything now. What do you want to pay for and to whom? Or what did you really want or want?
You said you bought a new computer with Windows 10 installed, meaning you already paid for it and Windows 10 is available and paid for on your computer. The only thing is that the person who installed it only activated the features of the Home version. Now you wanted the Pro version features. Is it so? If so, enable these settings.
You have already paid for it, what else do you want to pay?
And if you really want to pay, you don't have to ask anyone for permission?
I'm sorry, I really don't understand what you wanted to know then?
OK, pay whoever you want and exactly as much as you want, it's up to you, but again - what you asked in your first post is already on your computer, and if you bought a new computer, you've already paid for it. There is even more things, for what You have already paid and about what You most likely don't know. Good bye, good luck.