Hi, this article might help:
http://lifehacker.com/5986883/how-to-combine-multiple-hard-drives-into-one-volume-for-cheap-high-capacity-storage
Note that some of the options described within the link might not be applicable to you if your Windows OS doesn't support it. And you are advised to test those options out at your own risk.
Alternatively, just buy a bigger capacity drive that is enough to hold all the data in one drive.
http://lifehacker.com/5986883/how-to-combine-multiple-hard-drives-into-one-volume-for-cheap-high-capacity-storage
Note that some of the options described within the link might not be applicable to you if your Windows OS doesn't support it. And you are advised to test those options out at your own risk.
Alternatively, just buy a bigger capacity drive that is enough to hold all the data in one drive.