Just to get this out of the way.
If you already have an LGA1151 motherboard, that does not mean that all LGA1151 CPUs are supported.
LGA1151 v1 = 100 and 200 series motherboards (Z170, H110, Z270, B150, etc) Support for 6th and 7th generation Intel CPUs (i3-6100, i3-7100
LGA1151 v2 = 300 series motherboards(Z370, Z390, H310, B360, etc) Support for 8th and 9th generation Intel CPUs (i3-8100, i3-9100)