What can be done to reduce the level of triglycerides & higher the level of hdl-cholesterol?

REDUCE CARBS/OMEGA 3: Reduce crbs especially simple carbs like sucrose, fructose and glucose, alcohol and consume oily fish like salmon high in omega 3 to bring HDL up fish high in omega three like salmon, sardines, herring, tuna, oatmealfoods containing Niacin like chicken, nuts and dairy products.And alcohol in moderation will increase yourhdl.

Depends on Cause: High triglycerides (tg's) are the most common cause of low HDL cholesterol. Obesity , pre diabetes, diabetes, "insulin resistance" and high carb diets are often associated with this condition, so reversing these can often improve both tg's and HDL cholesterol . Sometimes there is a genetic cause, so even small changes in diet can be helpful. In cases of severe tg elevation, meds may be needed