I have a table named students. the structure is given below

```
______________________________ 
AdmissionNo   RollNo   Name 
______________________________
1001              1     A  
1003              2     B  
1005              3     C  
1006              4     D  
1008              5     E  

```

---

Now i want to change rollno 4 to 2 and increment forthcoming numbers

so the result should be like below

```
-------------------------------
AdmissionNo   RollNo   Name
-------------------------------
1001              1     A  
1006              2     D  
1003              3     B  
1005              4     C  
1008              5     E  
-------------------------------- 

```

How to attain this using sql Query.

Note: Question Edited as per 'The Impaler' said.Admission number is not changing.only Roll no change. The values in table are examples actual values are hundreds of records.