For transfers click on the transfers icon on the left side of the screen.
Click on the yellow box of the player you want to take out, then click on the player you want to bring in, making sure he plays in the same position.
when finished just click on confirm transfers.
You get one free transfer per gameweek, then you lose 4 points for each additional transfer you make.
You do though get one transfer wildcard, which you can do once during the season. This allows you to make as many transfers as you wish in one gameweek, without losing any points. To use this you just click on the wildcard option when confirming transfers.
current standings: