This one is the simple one..
0. Click the textbox.
1. On the right side of your screen, you can see the Solution Explorer and the Properties tab.
2. Kindly search for the Property "Text Align" on the Properties tab.
3. There you are, you can set it if you want it aligned on the left side, right side or on the center.
If you want it to be more complicated (or do it on runtime), you can code it.
This is the code...
textbox1.TextAlign=HorizontalAlignment.Center