I double clicked on EIP
in register window,but seems un-editable.
Why is EIP
special?How can I change it?
Find the location you want to set your EIP to, right click and select "New Origin Here". This will reset the EIP to the new address. You can confirm this by inspecting the registers at the top right.
In addition to the reply above, the EIP is basically the pointer to where the current line of execution is. It's used to keep a record of which instruction the program is executing in memory.