Bitcoins price is based on supply and demand on the market.More demand higher price more supply down price.Yes you can manipulate bitcoins price if you hold a huge supply or supply that may be enough to sell or buy in the current market status
by regulating demand and supply that means you can manipulate the price of bitcoin. but this time because bitcoin users have very much of course to manipulate demand and supply has been very difficult dude
The manipulation of supply just can be done by the bitcoin exchange site , and look at the chinese exchange in the previous time too many the ghost volume in his circulation and after the PBOC had done the audit and all of the fake volume was disappearing. and it will need a lot of the effort to do that.