Here's a link to the Vector API which shows you all the methods available to a Vector. http://java.sun.com/j2se/1.3/docs/ap...il/Vector.html
You should be able to find methods here that'll help you solve your problem, but I'll give you some pseudo code as well.
1. Get the first element of the vector and store it in an int variable. Look at the methods firstElement
2. Take the value returned in step 1. and add to it.
3. Replace the first value of the Vector with the new value from step 2. Look at the methods set
There's other ways to solve this problem as well, but this will hopefully give you a good starting point.