Hello !

Since a few weeks, my low frets have started to buzz.
I tried to raise the string action in order to suppress those buzzes, but now I have trouble fretting the strings on most of the fretboard. Now, they're simply too high, whilst they are at the right level over the low frets. It's really hard to play, not comfortable at all, and the sound is not as "deep" as before.

So it leads me to think that the neck is somehow too bowed, or not enough. I don't really know much about truss rod adjustments, so I'm asking for your help.

Here's a (very) exaggerated drawing of what seems to be my problem. I think the strings are not parallel enough to be used correctly.
http://i.img***ur.com/8UIAHlW.png?1 (remove the *)

If you could tell me what do you think of this issue : is the neck too bowed or not enough ? Or is it another problem altogether (though I'm pretty sure it's related to the neck's shape). And if that is the case, should I turn the screw clockwise or counter-clockwise ?

By the way, it's a cheap old guitar, but I'd rather do it by myself, I don't want to pay and wait 2 weeks to a professional if I can do it myself. I'm conscious this can damage the guitar permanently if done wrong, so I will take it slowly (on several days if needed).

Thanks in advance for your help !
Sounds like you have some back bow. You can check by either using a staight edge and laying it down the neck or just by holding the body of the guitar and looking down the neck toward the headstock, use the strings as your straight edge. You should be able to see what the neck is doing. Then go from there.
Thank you !

When looking down the neck, I can see a slight "peak" (Top of the curve, I don't know the word in English) under the twelfth fret and it goes down on either side of the neck.
So I assume you're very probably right !

According to this, should I release pressure on the truss rod ? And (stupid question again) : should I turn the screw clockwise or counter-clockwise in order to do that ?
You need to loosen the truss rod. Clockwise or counter clock wise depends from where you are viewing the truss rod from. If you are looking at the truss rod from the headstock down to the bridge, then you turn counter clockwise. If you're viewing the truss rod from the bridge to the headstock (playing position), then clockwise.
Thank you very much, that's going to help a lot !

I also heard that the neck shouldnt't be too flat, does it need to be slightly bowed or back bowed ?
Quote by Derpyy

I also heard that the neck shouldnt't be too flat, does it need to be slightly bowed or back bowed ?

There should be a slight relief (bow). But essentially you should keep it as straight as you can without losing playability.
Just turn the truss rod 1/8-1/4 turn and let the neck settle.
Personally I'd leave it for a good couple of hours, but others say let it settle over night.
Anyway.. if it plays nice..leave it...if it's still got a back bow you can give it another slight turn...rince and repeat.

Since you messed about with the string action, I'd recommend you get that sorted now as well...and change to a new set of strings and set your intonation while you're at it!
Things with strings:
Ibanez J.Custom, Prestiges, RG8, SR5 bass etc
LP's, Strat, Tele
ENGL Retro Tube 50
5150 III 50W
Orange Terror Bass
Thank you, I will take care of this this weekend when I have free time !
My current strings are brand new so they shouldn't be a problem. And there's plenty of tutorials so I guess I will manage.
Thank you all again for the support, I can't wait to get the same intonation as before.