if you want to stick with W8, make sure it is installed in Primary Partition (Drive C: )... So You can delete or format the other partition from where you installed other OS in Disc Management.
I have created two partitions on the SSD. So, I installed Windows 7 first, which take up the first partition, then I installed Windows 8. So if I delete the first partition, the 2nd partition (Windows 8) will still work fine?