How do you remove a broken bolt from an engine block?

The head of a bolt broke off of the bolt shaft on my engine block while I was replacing my water pump. What is the procedure to remove it? Do I need to retread the block? What tools do I use and is it worth trying to do it myself (I have no experience doing this)? Also, how much would it cost to have it fixed... show more The head of a bolt broke off of the bolt shaft on my engine block while I was replacing my water pump. What is the procedure to remove it? Do I need to retread the block? What tools do I use and is it worth trying to do it myself (I have no experience doing this)? Also, how much would it cost to have it fixed professionally? The bolt is very easy to access.

Thanks

1990 XJ 4.0 engine
Update: John, the pump only has 4 bolts. That probably won't be an option for me as the pump might easily leak or distort.
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