Literally, a "notch" is a small, narrow, V-shaped cut. Often, it means a small notch carved with a knife in a piece of wood. However, a narrow mountain pass can also be called a notch.

Sometimes, there is a control on a piece of machinery that adjusts something. For example, the throttle on a gasoline engine lets more or less gasoline flow into the engine and makes the engine run faster or slower. Such a control might just be held in place by friction, but the engine vibration might make it slip. So, sometimes the control uses a spring mechanism and a set of notches. Instead of being able to turn the knob continuously, there might be ten notches numbered 1 to 10. The control falls into one notch and sticks there. You can click it into another notch. You can only set it to ten different settings, but it is going to stay held at that setting even if there is a lot of engine vibration. 

"Take it up a notch" means to move the throttle, say, from 5 to 6. "Take it down a notch" means to move it, say, from 5 to 4. Thus, "a notch" means "the smallest adjustment that can be made."

"Take it up a notch" means "increase it just a little." 

The proper engineering term for this kind of notch is "a detent."

Here's a real example of use in a literal sense, in a diesel locomotive:

https://science.howstuffworks.com/transport/engines-equipment/diesel-locomotive10.htm

"The throttle control has eight positions, plus an idle position. Each of the throttle positions is called a "notch." Notch 1 is the slowest speed, and notch 8 is the highest speed. To get the train moving, the engineer releases the brakes and puts the throttle into notch 1."

Daniel,

I noticed that somebody was downvoting several of your posts.  I voted some back up. Sometimes I wish people would be clearer in giving feedback and tell you what they did not like about your posts.  I want to give you feedback that I assume that someone's disapproval of your posts was probably related to how very casual you write. 

In my opinion, the general normal here is to make an effort to use standard English when you are asking for help with English.  We do not expect perfection but a lot of regular native English posters here have written in the past that if someone wants help with their English they expect that they should also show some effort to avoid the texting type of language, to capitalize their "I"s, etc.  Your style is soooo informal that I wanted to let you know that I think you are not conforming to what I perceive as the general norms of the people who are most active here.  If that is not why someone downvoted your topic, I personally am curious why they would do so.   

Oh Jerry, but the urban dictionary is fun and useful for learning what SOME people think things mean!  I honestly do find it helpful to go look up things to get possibilities for what someone might mean--- especially when I am trying to understand rap songs or have been listening to teenagers.

Daniel wrote:  ".But i've doggedly trolled three dics"  Certainly a very informal sentence and my first reaction was "did he really say that?and surely he did not mean what first went through my mind what to "troll"  and "dics" might mean.  Obviously, I read on and learned that "dics"  was short for dictionary. 

Daniel--- dics might not be the best abbreviation for dictionary.  It can be used to mean a lot of different things, and I do not think I am alone in the tendency for my mind to "go to the gutter"  when things are ambiguous, thinking it was a typo. .  https://www.urbandictionary.com/define.php?term=dic

You could have tried the Merriam Webster:

https://www.merriam-webster.com/dictionary/notch