So how do I loosen those lines up? The lazy jacks are the only thing holding the boom up. I have tried adjusting them where the cleat is in the middle of the boom, but then the boom seems to sag quite a bit. Again I'm new to sailing and am still figuring things out.
The sail itself should 'hold the boom up'.. when the sail is fully hoisted the lazy jacks ought to slacken off, if they don't then you ease that central line to create slack. If they are tight while you're sailing they will interfere with your mainsheet setting. Keep an eye on that, if you sheet the main in harder (say to go upwind) your may find your jacks tightening up again.. they'll need to be eased then too.
So, based on your picture, your halyard is too soft, ie the main is not fully hoisted. Depending on the boat's/sail size you may need a winch to get that done. Head to wind, you should have a vertical wrinkle in the sail parallel to and along the mast once it's all the way up (rough guide). In heavier breeze this should be tighter, in lighter, looser, but that variation is most often dealt with by a cunningham adjustment which you don't have.. You may have a black band around the mast 6 inches to a foot below the top.. if you do that's where the top of the sail is meant to end up.
The other adjustment that looks too loose is your 'outhaul'.. it's the line that stretches the foot of the sail along the boom. All those wrinkles there shoud be taken out. Again, tighter for heavier air and looser for light, but not as loose as it looks now. There will be an adjustment for that, it may be internal to the boom and exit somewhere forward on the boom or at the gooseneck (or may be run aft to the cockpit) btw.. what boat is it? Offset companionway, I see, but I don't recognize it in that pic - 30 ish feet??
Finally your reef clew lines may need adjustment once the sail is properly set, they should be slack enough not to interfere with the leech curve of the sail.
Also, you do have a vang and that's good.. when the wind pipes up the sail will tend to lift the boom further, esp with the sheet eased.. the vang will let you bring it back down and retension the leech as appropriate..
If some of these terms are confusing you, get yourself a beginner's book and try to learn some of the terminology - it's part of this game and will allow you to properly digest whatever help you get from members here..