Eassos PartitionGuru Free provides comprehensive functions for partition management and it is able to convert MBR (master boot record) to GUID partition table (GPT) without losing data.
Step 1: Get PartitionGuru started by double clicking the icon.
Step 2: Select the disk that needs to be conveted, and click menu items “Disk” and “Convert To GUID Partition Table”.
Step 3: Click “OK” on the poped-up dialogue box .
Step 4: Click “Save All” button to save new partition table to disk.
Important：Make sure whether your computer supports GUID partition table before the conversion; if the operating system doesn’t support GUID partition table, after conversion the disk will become inaccessible.
Download PartitionGuru from here: http://www.eassos.com/partitionguru.php