and throw the 8Gb in the bin? ================== Well, yes. Get rid of it or hopefully give to someone who can use it.  If you install a perfect matched pair of compatible memory DIMMs, it will run at the system's intended stock speed, and also in DUAL-CHANNEL.  Get CPUID's CPU-Z to analyze system and track your progress. 
Hi guys, I am pretty new to computer. I am trying to add more ram to my current PC.  My PC is  ALIENWARE - Aurora R9 Intel® Core™ i7 GTX 1660 Ti Gaming PC - 1 TB HDD & 256 GB SSD. My Current ram is the default one [8Gb] which runs 2666MHz. Should I get the Dell Memory Upgrade - 16GB - 2Rx8 DDR4 UDIMM 3200MHz XMP? Is it ok to install both in the dual channel [With the 16Gb in the main slot and 8Gb in the second slot] or just install the 16Gb instead and throw the 8Gb in the bin? Thank you for reading. 
Increasing ram in my ALIENWARE - Aurora R9 PC.