Changing (increasing) bid limits

I placed a bid on an auction item, but I need to increase the max bid in case I am not around when the auction closes.  Since the current high bid (my own) does not exceed my max bid, but does not meet the reserve - how can I change my bid?

example

you bid $100 - no one else bids you raise your bid to $1000 - someone bids 95 you auto out bid him to 100 - he bids 745 - you auto bid 765 +/- he bids 1000 - you are still the high bid - he bids 1050 +/- you loose

Which is exactly why I need to raise my max bid, but once the initial bid has been made - I can't seem to revise my max.  Perhaps you could delete my bid and I can start over.