There is no DDR5 RAM. Current memory standard is DDR3 RAM maxing out at 2133mhz speed, using DIMM slots. Video Cards use a similar, but incompatible GDDR5 standard, using PCI-E slots. DDR4 standard will be available in the near future, but not today.
And no, even if they release DDR5 one day for PC, you would have to replace the whole motherboard because the RAM slots are different between generations (for example, you can't fit DDR3 on a DDR2 motherboard).