after some time I may feel that pool is very low and I want to cancel my transaction and it may lead to dealt of my transaction in about 3 to 4 hours. -snip-
Sorry but this doesn't make sense, please elaborate.
After getting 1 confirmation, it's now included in the blockchain and the subsequent confirmation is just based from how fast the next blocks are being mined.
It's not just based from the pool that mined the block where your transaction, any new blocks mined will add 1 confirmation to your confirmed transaction.
If you can somehow cancel it (
extremely hard), you wont gain any "
speed-up" at all.