Drain plug remove and replace on DS II

I've tried adding pics, but very difficult. Will try to describe.
Drain plug on bottom has been plugged with caulk/silicon. Top of same plug in back of cockpit on floor is all corroded. How do I fix this/remove this? And then replace?
I have ordered a new drain plug. D&R Marine said that I might have to enlarge the hole to 1 inch.
Can anyone let me know what to expect as I get into there to do this replacement?
Many thanks.
Hal
Drain plug on bottom has been plugged with caulk/silicon. Top of same plug in back of cockpit on floor is all corroded. How do I fix this/remove this? And then replace?
I have ordered a new drain plug. D&R Marine said that I might have to enlarge the hole to 1 inch.
Can anyone let me know what to expect as I get into there to do this replacement?
Many thanks.
Hal