1) Buy an extra drive, internal or external.
2) If you don't have any, download backup software
3) Backup your OS drive. Test your backup. If you did a disk image, try booting from the backup.
4) Once you are sure that the backup is good, take out the current drives, build a RAID from the new drives, and restore your backup.
Now, some unasked-for advice. RAID0 is dangerous; you should always have tested backups. DO NOT put SSDs in any level of RAID. They will not receive the TRIM command and will slow down significantly over time.
If you need 480 GB of space, either buy a 480 GB SSD or have the two SSDs separate. Install the OS to one; install large games or applications to the other.
As I said above, I strongly recommend
1) Doing it with a backup-and-restore process. This can be done to leave you on one of the same ports, if you like.
2) Not putting your SSDs into RAID.
That motherboard has seven sata 2 ports according to what I read. You are probably using the two the GIGABYTE SATA II chip; there are also five supported by the chipset itself. Were I you, I would put the new OS SSD on one of the chipset ports rather than a port from an add-on chip.
I second not using RAID with SSDs. The benefit does not outweigh the risks. If you have 2 SSDs already, just make them 2 separate drives (OS and Games etc). If you haven't purchased them, just buy 1 larger SSD. Larger SSDs tend to be faster than an otherwise identical smaller one anyway.