I need to modify locations of data in an excel worksheet!

For example, I am utilising 4 columns (A,B,C,D)
In row 1, I have A storing "Test1", B storing "Test2"
On the 2nd row, I have C storing "Test3", D storing "Test4"

When I execute my VB code, the data in row 1 column B has to be moved below A, and D below C.

How do I modify locations? And how should i access the worksheet? Any article which can show me how to pin point hte locations?