i think it's the same as my zenbook UX303lb.
assuming the above is true, you have to go to the asus download page and get the program that does this automatically.

addendum:
i just went to your UX52(?) download site : https://www.asus.com/Laptops/UX52VS/HelpDesk_Download/
here it is:

Version V1.3.118.0
2015/08/3110.21 MBytes
ExpressCache (For Windows 10 Upgrade)
If you upgrade OS from Win8.1 to Win10 before 25th Auguest 2015, please follow below steps to update ExpressCache:
1. Download newer version of Express Cache.
2. Run ECWin10Cleanup.exe via administrative command prompt
3. Run ExpressCacheSetup.exe
4. Reboot your system.
!! DO NOT reboot between step 2 and step3.

DOWNLOADSHOW MORE DESCRIPTION

(lol at Auguest)

this thing does the magic. and! if you're clean reinstalling, ignore the steps 1-4 above. just install it outright then restart.

mind you, this "caching" technology is far from perfect. the most it does on my UX303lb is to speed up boot times, and that only happens after couple restarts.
if my suspicion is correct, asus has since moved away from this too, and would rather implement true SSD or SSD boot / HDD mass storage combo.