Just bought Imac 27" struggling with a few settings

Ive just bought a 27" Imac , its dual booted to run on either OS or Windows , to be honest I will rarely use windows but its always there if I need it , when I switch on it automatically runs Windows in which I have to press the alt key and restart to have the option to run Mac os , is there anything I can adjust so that when I switch on it will run Mac os from the start.

Another thing is im struggling to use all of the full screen on Safari , ive tried using the different display resolutions but its still not spread across the full screen , what will I need to adjust so all the screen is used

Thanks
Gary

Can't answer your dual-boot question since I didn't have that setup..I do, however, have a 27" iMac and you want to run it at the default 2560x1440 resolution. To get into the full screen mode, instead of hitting the normal maximize button, you can hit the two arrows running opposite on the right side in Safari..

It's the small icon on the right in the image below.

Thanks mate just done it , the writing is now very small how do I increase the size

You can't really increase the overall size within OS X, but you can increase the text size in each application. In Safari, you can use CMD and the + key to increase, CMD and the - key to decrease the text size..

click the apple in the top left corner then system preferences under startup disk change to osx and then click apply.

you can also do it in windows in control panel and change the startup disk to whatever you want windows by default or mac.

Go into System Preferences > Startup Disk and you can restart BootCamp from there. When in Windows, in the bottom bar there is an icon for Bluetooth, BootCamp etc Control Panels. Select BootCamp and restart in OS X.