At 5'8" and 300lbs, can you see any abs at all? Maybe even the top 2? If not at least the top 2, sorry to say but you're fat as fuck. Saying that, if you keep on the sauce and are committed to getting abs, proper eating habits can get you to prob 215 with a nice six pac and look a million times better than 300lb and a 42+ inch waist. Start with this: take your normal size plate of food, and scrape 20% away (don't eat it/maybe store for later). Give that several weeks to kick in and when your fat loss plateaus adjust your macros.