PLEASE don't try to repair a part of the screen (glass or glass+digitizer). It takes more than "confidence in your tech skills", it takes learning by doing (and destroying a few bad screens in the process). If you do it yourself, you're most likely going to end up trying to find a shop willing to fix a phone you've already worked on (since they're responsible for any damage they didn't find, it's going to take a lot of hours - read money - to find everything you might have broken before they start replacing the screen, you'll balk at paying almost as much as a new phone would cost, so they'll be left selling a used phone for less than the repair bill - and losing money).
If you want to replace the whole screen assembly (it's not THAT much more expensive), make sure you're comfortable with what's needed, after watching a few videos. You'll need a good heat gun (a hair drier won't do it), some hand tools, a very steady hand (one slip, the screwdriver going through the motherboard, and you might as well throw the phone out) and a LOT of patience.
After many years of repairing cellphones, I've found VERY few people who don't work in the repair business who can replace glass or a digitizer, and not many more who can replace a screen - successfully, the first time. (We used to train new techs on phones not worth repairing - like replacing the screen on a phone that had the screen punched clear through - so if they broke the screen it didn't matter. It takes about 5 screens to learn. And to replace the glass - some people just can't get it right, no matter how much they try. The entire surface of the glass has to be just hot enough to soften the adhesive enough without damaging the digitizer. It's like sticking a needle through only the first 3 layers of someone's finger - with one hand and your eyes closed. If you don't have the "sense", you won't do it. (Too cold and the glass and digitizer snap. Too warm and the digitizer fries. Uneven heating and the glass snaps, and could damage the digitizer at that point. It's really not for amateurs.)
Having the screen replaced is a LOT cheaper than having the phone fixed after you've broken it, then having the screen replaced. (It would still be worth the doing for a Mega - it's not a cheap phone to replace. But why spend a few hundred dollars extra?)
anyway, when I use the buttons on the side of my phone it works but the screen itself is unresponsive sometimes, like where it is cracked it doesn't work at all but near the top of the phone where it is only cracked a little it responds a bit. I don't know what to do! please help me 
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