Either use substitute or a macro [I guess u are using vim,u can try the same for vi but am not sure if it works]
Suppose you have the number in the third column
:map K 2wxj
[Means Move 2words - 2w , delete the first character x , and go to next line j]
After this just press on the K key continuosly for the task to be done.
Try this too
:map K 2wxjK
This will recurse and u will have to interrupt when it reaches the last few lines.
Substitute needs regex search and replace in the format
:% substitute /patter/replace/g
If u are still not able to do the task ,paste a part of file in this post.