Does flax seed help to lower cholestrol. If yes, how should we consume and what quantity should we consume?

No requirement. There is not a specific daily recommended requirement for flax seed oil. Adequate intake of omega – 3 fatty acids is around 1.1 to 1.6 grams/ day for an adult. If you elect to get it through flaxseed- 1 tbsp of ground flaxseed has about 1.6 grams of omega 3 fatty acids.
Yes. Flax seed has linoleic acid which is anti- inflammatory and helps lower LDL cholesterol - flaxseed lowered total cholesterol by 6.9 percent and LDL (bad) cholesterol by 14.7 percent. However, only ground flaxseed has such effects on cholesterol; whole flaxseed is not digestible. Exact amount need to be adjusted with your lab value with your md.