I bought an Asus transformer trio (2015) which I opened only after 4 years (2019), so a Windows 10 upgrade was in order. After the update, partition setup was like this:

Recovery | EFI Boot | MS Reserved | OS

I wanted to recover disk space by deleting RECOVERY partition from the new SSD I had cloned it into and merge it with the OS partition, here was my solution:

- Delete RECOVERY partition with mini partition tool.

- Image the resulting partition setup sans RECOVERY, UNALLOCATED SPACE in lieu on a USB disk.

- Recover image to my SSD via macrium reflect, with method of dragging one partition at a time to destination disk in this order: EFI Boot | MS Reserve | OS.

- What will remain at the left/end is the UNALLOCATED SPACE which I was able to merge back to the OS partition with ease using mini partition tool.

Hope that Helps!