Craigsmith88 you need to change the config.txt file in the root of the sd-card.
i have a waveshare 5 inch hdmi screen and my config.txt looks like this:
uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1
disable_overscan=1
uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=2
hdmi_mode=87
hdmi_cvt 800 480 60 6 0 0 0
max_usb_current=1
comment to get jack audio
hdmi_drive=1
Using /etc/modules is deprecated and no longer supported on 4.4 kernel
So manually enable audio
dtparam=audio=on
config_hdmi_boost=0
force hdmi while the tv can take time before sending the signal on the hdmi output
#hdmi_force_hotplug=1
uncomment for composite PAL
#sdtv_mode=2
uncomment if you have slow sound issues on composite output
#audio_pwm_mode=0
uncomment for lirc-rpi
#dtoverlay=lirc-rpi
if you plug your tv at the same time as your rpi and that the rpi switches from the hdmi or give a low resolution because tv had no enough time to initialize it
boot_delay=3
uncomment if you don't want the rainbow at startup
disable_splash=1
Overclock
gpu_mem_256=128
gpu_mem_512=256
gpu_mem_1024=384
avoid_safe_mode=1
kernel=boot/linux
initramfs boot/initrd.gz
enable UART (required for for retroflag)
affect rpi performances
enable_uart=1
