re:
Sure it's possible! How you want to do it may depend on the amount of data to transfer, your bandwidth, and your available hard drive space. I believe the easiest way would be to sync the data in the old OneDrive account to a local folder, and then upload them to the new one.
I have a very important folder in Google Drive that I occasionally back up to OneDrive for redundancy. I have both accounts synced to local folders on my PC. Every so often I just copy and paste the folder from one to the other. You could do something similar to move your files from one account to the other.