Windows 8.1 pro not activated

Hi, 

I have Dell Inspiron 15 , i had windows 8 activated .. and i upgraded it to windows 8.1 for free from the store. and it was still activated. 

and after about 2 weeks it's upgraded automatically to windows 8.1 pro and it asks me about the activation code.

i want to downgrade to 8.1 but activated , is the possible ??

Thanks in advance