re-setting a TextView height programmatically

Pragmatically you can set textview height like:

private TextView mTxtView;
int height = 50; //your textview height
mTxtView.getLayoutParams().height = height;

you can dynamically set width and height of textview by

private TextView mTxtView;
private int screenWidth, screenHeight;
Display display = getWindowManager().getDefaultDisplay(); 
    screenWidth = display.getWidth();
    screenHeight = display.getHeight();


LayoutParams params = mTxtView.getLayoutParams();
    params.width = screenWidth-30;
    mTxtView.setLayoutParams(params);

You should change it via LayoutParams:

LayoutParams params = (LayoutParams) textView.getLayoutParams();
params.height = 70;
textView.setLayoutParams(params);

EDIT

You should not use sizes in pixels in you code, use dimensions for this:

dimens.xml:

<dimen name="text_view_height">50dp</dimen>

In code:

params.height = getResources().getDimensionPixelSize(R.dimen.text_view_height);