In Disk Management, assign the System volume a drive letter of M:
Then copy the bootmgr file from root of M: to C:
Then copy the boot folder from root of M: to C:, and skip over the files it says it can not copy.
Open an elevated (Admin) command prompt to run this command (you can copy/paste with mouse):
bcdedit /export C:\boot\bcd
When that is successful, go to Disk Management and set C: as the active partition.
Reboot. Check Disk Management to make sure that C: is now also the System volume.
If so, you can format M: then use any utility that can merge volumes/partitions. I recommend Acronis Disk Director but there are many that can do it.
Once this is all done, you can convert the disk to a basic disk and then after, proceed to install Windows 8.
Here seems to be another freeware tool to convert disk types, but I have never used it, so choice to use or not is yours of course. Just giving choice in addition to Calico's seemingly excellent suggestion (I have never tried that either):
Free convert dynamic disk to basic disk without data loss under windows 2000/XP/Vista/7/8 and Server 2000/2003/2008 32 bit and 64 bit.