Using Easus Partition Manager you can definitely move partitions around and merge them. I've done it several times and EPM is wonderful for that.
First you tell EPM to "delete" the partition. It doesn't actually make it disappear but empties it and makes it into an unused, unassigned partition. You then use EPM to drag and drop the partition to where you want it, just to the right of the C: partition. You then tell EPM to merge the now unused partition with the C: partition. Once you've told EPM what you want it to do you tell it to execute the commands.
EPM now reboots the computer and performs all the heavy lifting. When the computer boots back up, you now have an enlarged C: partition.
You might have to then run Disk Manager and tell C: to extend to occupy that new space. No reboot required.
EPM is great software and is what I always use when I need to do any work on on a Workstation OS like Win10, Win8, or Win7. It's free and it doesn't get any better than that.
Jonathan