RAID 0 is what you're looking for. But....
JBOD is what you are looking to do, not really a raid solution. Also if the disk are clean (no volumes) you can create a spanning volume over both disk (in windows).
One word of caution, back up. Use a cloud service to back up the data on the volume you end up using. If one disk fails you will lose all the information from the spanning volume. If one disk fails in a JBOD setup, you just lose the info from that failed disk.
Again, BACK UP your data.