Awful slowdown on Asus Zenbook

Hello,

I have an Asus Zenbook ux32a. It's coming up for three years old now and suffers awful slowdown. I fitted extra RAM, 69 GB from 185 GB are used on the hard drive, performance is usually 10-40% from CPU and 30-40% of memory and I've wiped it clean and rebooted several times but still suffer very bad slowdown.

I use the following programs: Memoq, office 2013, Bitdefender

Does anyone have any suggestions where the problem may lie?

Thanks in advance!