Does eating high cholesterol low fat food like crab elevate good or bad blood cholesterol?

Both: It increases both the good and bad (hdl and ldl) cholesterol. For most, that results in a better or no-worse LDL to HDL ratio. Those foods are better for you than the saturated fats (lard, palm, coconut, etc.) which raise the bad and lower the good (bad for your ratio).

Carbs increase ldl: The latest info in that too many refined sugars and animal fat can increase LDL to help decrease cholesterol be plant based (9cups of veggies/fruits/day), good grains such as brown rice, quinoa, millet, oatmeal, and lean protein such as poultry & fish are better. Limit dairy as well since that is an animal fat.

Maybe neither: Plant and seafood sterols compete for sites used to synthesize cholesterol (found only in animals). Their presence in diet may actually reduce both total and bad cholesterol with little to no change in hdl. Omega 3 unsaturated fatty acids also compete for cholesterol synthesis. Seafood is better than red meat, and should be included in diet.