Hi and thanks for reaching out. My name is William. I'm a Windows technical expert. I'll be happy to help you out today.
Connect both drives to the same computer > open 2 instances of file explorer > copy the files from the 1TB drive to the 2TB drive. You may then quick format the old 1TB drive to make all the space available again.
Note, although you can move the data instead of copy, I recommend against it. I have done a few data migrations and have seen a few done by co-workers where move was done instead of copy and the process would "hiccup" leaving both source and destination missing data.