After effects

My scrolling/rolling credits preset uses a check box to change horizontal movement to vertical and has a slider to adjust the number of pixels per frame. I'll share the preset and the expression with you. 

Your expression is ok. The description is not accurate. It should look like this:

rate = 2 ; //value in pixels per frame
value - [0,rate*timeToFrames(time)]

If you just want to modify the expression to make the layer move faster change the 2 to a 4. 

Here is the basic expression that I use:

moveDistance = 6; // distance in pixels per frame
startTime = time - thisLayer.inPoint;
frameCount = startTime / thisComp.frameDuration;
pixPerFrame = frameCount * moveDistance;
[value[0], value[1] - pixPerFrame];

Change the move distance and change the speed. I added the start time to make it easier to set the starting position of the layer. Your expression starts moving the layer from the first frame of the comp instead of the in-point of the layer.

The animation preset adds a slider and an expression so you can use the same preset for credit rolls or credit crawls. You can download it by clicking here. Download it, save it to your custom presets folder, and then use the Animation/Apply Animation Preset menu to browse to the preset and apply it to your Null. 

The technique depends on how the roll (credits usually roll from the bottom to the top of the screen). You have to be careful about speed or you will end up with Judder and the titles will look terrible. The credits layer should move exactly an even number of pixels per frame. If they are moving 6.32 pixels per frame the edges are going to look terrible, especially if the type is small or thin.

Give us the workflow and let us see a screenshot with the modified properties of your credits layer revealed. Just press 'uu' and embed the whole screenshot using the toolbar. Do not use the Drag And Drop section below the forum post. We won't be able to see your screenshot.

You should give more info, at least a screenshot of your workspace including the timeline panel with visible keyframes of your animated layers, but generally: narrow your keyframes to each other