Convert MBR to GPT on already dual-booted system without data loss

I have dual booted system Ubuntu 16.04 and Windows 8 with Grub2. I plan to convert MBR to GPT. I was looking at AOMEI Partition Assistant and just need to know whether it will preserve my dual boot. Also if I have any other better alternatives?

Here's how my partitions look like:

The bulk of your OS installations should be fine after the conversion, providing the software does what it should; HOWEVER, boot loaders are different for MBR and GPT disks. I'm not familiar with AOMEI's partition table conversion tools, but assuming it converts only the partition table, the boot loader differences mean that your disk will be rendered unbootable after the conversion. If AOMEI does something to boot loaders, the disk might end up booting in one or both OSes, but this is really the tricky part of the conversion, so even if the tool claims to handle it, I wouldn't be surprised if it didn't work.

It is possible to do an MBR-to-GPT conversion and keep your OS(es) bootable, but extra steps are likely to be required. For Windows, see this page for details. For Ubuntu, the easiest approach may be to use Boot Repair. Note, however, that Windows will boot from a GPT disk only if your computer has an Extensible Firmware Interface (EFI) firmware (or Unified EFI, which is EFI 2.x). Most computers introduced since mid-2011 have EFIs, so if your computer is less than about five years old, you should be OK on that score. If your computer is older than that, though, chances are you won't get Windows booting after such a conversion -- at least, not easily. If your computer is in the transition period, research its capabilities carefully.

Even if your computer has an EFI, you should heed the wisdom of the old saying, "if it ain't broke, don't fix it." Converting from MBR to GPT (and therefore from BIOS-mode to EFI-mode booting) is risky; about a million different things can go wrong in such a conversion, resulting in anything from a few minutes' extra effort to the total and catastrophic loss of all data on your computer. The worst of these consequences are unlikely, but if you don't need to make this conversion, why risk it? Your question provides no motivation for making the change, so that question isn't really rhetorical -- you may have a valid motivation that you haven't described. If you're doing this on a whim or because you've heard GPT is "better" than MBR, though, I strongly advise against such a conversion. (GPT does have advantages over MBR, but those advantages are not worth risking the hassle of such a conversion in most cases.)