Nope,
First of all, don't mine bitcoin with a CPU or a GPU, only latest gen ASIC's.
Secondly, your own hashrate has very little impact on the difficulty. The difficulty is network-wide and is based on the average time between the blocks during the previous retarget period.
If the combined hashrate of all miners goes up, the average time between the blocks should go down, and during the next retarget the difficulty should go up to make sure the average time between 2 blocks is once again ~10 minutes.
s it true that GPU can increase the hashrate? If yes in what ways?
I have no idear what you mean... A cpu can create x sha256d hashes/s, a gpu y hashes/s and an asic z hashes/s
x<y<z
How does mining difficulty be reduced?
The difficulty will ONLY be reduced at the next retarget, and ONLY if the average time between the block during the last 2016 blocks was > 10 minutes. If you want a lower difficulty, you'll probably have to bribe big miners to turn off all their ASIC's?
Are mining difficulties of all crypto the different, I suppose yes, but I need further enlightenment about such differences.
yes, what is there to say... They all have their own blockchain, so there is no relation between a block found on the bitcoin network and one on the litecoin network (for example), so they each have an average time between their blocks, and a different difficulty
