VIDEO RAM is not replaceable VRAM is on the GPU. XMP is not available in all RAM and Overclocking is not USER DEMAND switchable.  Not all chipsets or Processors support overclocking. SPD (JEDEC) is just 2133 anything past that is marketing not actual performance. XMP is the overclocked Specification. Ram can say its 2666 compatible but not be XMP. The system can use XMP ram with a processor that supports XMP and the Bios Supporting XMP. This is not supported on All processors All Models All Speeds. Putting Faster Ram in a system that does not support overclocking will NOT make the ram or system run faster. You are falling victim to the Mhz myth. The speed rating is commonly labeled in DDR2/3/4 terms such as DDR4-2666. Along with speed ratings, RAM also has ratings for timing. This appears as a string of numbers such as 9-9-9-24. These numbers are indicators of latency which is the number of clock cycles it takes your RAM to do things. SPD stands for Serial Presence Detect, meaning that the motherboard expects the RAM to correspond to one of the JEDEC profiles for the configuration expected from that RAM type. XMP profiles are overclock profiles and not all ram supports that. XMP or Extreme Memory Profiles, is an Intel technology that allows you to change multiple memory settings by simply selecting a different profile, taking advantage of higher than standard memory speeds.  This is NOT guranteed for Joes crab shack ram and its NOT Guaranteed for All CPUS and ALL bios and ALL chipsets etc.  Its overclocking to speed that is more than standard.  It is faster but its not significantly faster meaning you are burning up your ram and cpu for a few percentage points more. [URL]    
I made the mistake of purchasing a Corsair 2x8 3200MHZ when Inspiron Desktop's only allocate for 2400 and 2666 MHZ however my memory is now at 2133, do I have to purchase a new ram or can I down clock the 3200 mhz to 2666 mhz? I'm on a Dell Inspiron 5680 
VRAM Memory Speed 3200mhz not showing on BIOS