The safest and easiest way is that using Dynamic Disk Converter convert a Dynamic Disk to Basic Disk. it can make up for the shortcoming of Windows Disk Management. By using it's able to convert dynamic into basic disk with NO DATA LOSS, and but this conversion back does not affect your operating system bootable. I think it deserves to be recommended a software, but it's a paid for solution.
1. Launch the Dynamic Disk Converter by using Administrator Privilege. It has a start screen, which could stay for a while if the dynamic disks on your system are too many. And then enter into the first page of wizard, here you click Next button to continue.
2. You select a dynamic disk which you want to convert to basic disk. And then click the Next button to check whether this conversion can be done successfully in the below screenshot:
3. Dynamic Disk Converter let you confirm the conversion operation. And then click then Proceed button to start this conversion process. After completing, you must restart your computer to take effect.
For detailed information of Dynamic Disk Converter, please visit the links: http://www.dynamic-disk.com/download.html