There is not much detail in this, its simple procedure, when using Partition magic it will ask u to choose the partition to merge, then what it does is that it removes the logical partition & moves the data to another area of the disk.
Points to remember is that u should have 20% free space at least & u should have good power backup for 20 mins, if there is power failure then u will be messed up, hence its said to have a data backup.
I dont need to take backup as I have 30mins backup on APC ups but since its important data I take the backup using arconis true image.