Installed 32GB of 2666MHz ram in my dell xps 15 9560 but bios shows it as 2400MHz

The memory controller is aboard the CPU - the memory speed is set by the CPU itself.  What model CPU do you have?

Not without replacing the mainboard - to which it is soldered.  And that will cost you likely over $400 just for the part - and will void your warranty.

The Kaby Lake Intel Core i5 7300HQ

Is there any way for me to upgrade the CPU

Well that stinks

Which RAM?

Userbenchmark shows certain good scores with XPS 15 9550 i7 and G.SKILL 2667 2x16GB RAM.

Most claim though that 2400 is the max that 9550/9560 will do. No idea if a hack is involved above. The processor and the RAM negotiate the clock and the latencies automatically, you can only see the outcome (check BIOS, CPU-Z, Userbenchmark). Mind RAM may run faster also at 2400 if it works with a lower latency. And that while faster RAM will produce the expected advantage in specific benchmarks and with particular RAM-intensive programs, but the overall performance is likely to improve by less than a percent, unlike going from a HDD to an SSD which is sensed by anyone, so there are likely better ways of spending money than on "premium" RAM.  

I got the ram from Crucial which was recommended by dell for the XPS 15 9560 - direct ram  link here: www.crucial.com/.../CT9926179 , dell upgrade compatibility site here: www.crucial.com/.../xps-15-(9560)

www.crucial.com/.../xps-15-(9560) - the list of compatible ram

www.crucial.com/.../CT9926179 - ram I bought

The i5-7300U maxes out at 2133 with DDR4 or 1866 with DDR3.

ark.intel.com/.../Intel-Core-i5-7300U-Processor-3M-Cache-up-to-3_50-GHz