First and foremost
Open Safari, search for Google Chrome, download and install, remove Safari from the Dock.
Screenshot defaults
Remove the drop-shadow from screenshots
Enter the following in Terminal, hit the return key after each line.
defaults write com.apple.screencapture disable-shadow true
killall SystemUIServer
To re-enable the shadow in screenshots replace true with false
Change Mac screenshots from png to jpg
Type the following in Terminal to set the default screenshot format to jpg
defaults write com.apple.screencapture type JPG
killall SystemUIServer