Increasing Enemy Speed

It's difficult to pinpoint exactly what the issue is since I have no reference to the default scoreCount value, but I am pretty confident the issue here is none of the if statement conditions are being met.

if ScoreManager.scoreCount is less than 10000 nothing will happen.

Since each of your conditions seem to run individually, you might as well put them in an if ... else with a default in case none of the above are reached.

A good place to start debugging this issue is also to add a breakpoints or even Debug.Log statements.

Technically, speed starts at 0 because you never set it, and by the looks of it, you destroy the object after the player (or this object) "levels up", so im assuming you respawn the enemy in a different script... In which these updates are not applied to (so it spawns with the default auto-assigned value of 0)

I would set a a base speed, something like 1f or 5f, initially however fast you want the enemey to move at "level 0", then on every level up, use += instead of =, since each one of your if-statements will only ever run once anyway, += will be far more accurate.

You also never use increaseSpeed and im not sure why its static in my opinion, though you could update one of your if-statements to look something like this:

 if (ScoreManager.scoreCount >= 10000 && ScoreManager.scoreCount < 20000 && level ==0) {
  
              speed += ((float)Random.Range (6, 10)) * Time.deltaTime; //Remember that speed is a float, and your ranges are integters, deltaTime is also a float, so for the most accurate calculations, you want to make sure everything is being processed as "floats" technically - hense (float) at the start, which converts the int result of Random.Range to a float.           
 
              glove.transform.Translate(Vector3.right * speed);
              //Destroy (gameObject,4); //Still not 100% sure why you need to destroy the object
              level++;
          }

Hope that helps.

thats because you put

 level++;

at update so everytime Update method called (which is at every frame) the level increased while your score don't. I think you should leave the level and use just score rank to determine your level like this

          if (ScoreManager.scoreCount >= 10000 && ScoreManager.scoreCount < 20000) level = 0;
          else if (ScoreManager.scoreCount >= 20000 && ScoreManager.scoreCount < 50000) level = 1;
          else if (ScoreManager.scoreCount > 50000) level = 3;

Then you can if-else statement with this

 ...
         if(level ==1) {
              level++;
              speed = (Random.Range (6, 10)) * Time.deltaTime;            
              //float change = (speed+=increaseSpeed ) * Time.deltaTime;
              glove.transform.Translate(Vector3.right * speed);
              Destroy (gameObject,4);
          }
 ...

or you can just put the statement inside the previous if-else statement. Hope this help and sorry if my english is not good