You can run a live session to get the feeling of how Ubuntu will work when installed, how the hardware is supported (or not) out of the box, without actually installing or making changes. For that you can use a few different tools to prepared the USB stick.
Rufus is good but pay attention to the options: Select GPT/UEFI before burning the ISO. The reason is ASUS X456UF has UEFI instead of the old BIOS, booting and installing in UEFI mode is preferable. Also recommended and related to this "UEFI vs BIOS" theme is to open UEFI settings and disabling any CSM/Legacy options (the factory installed Windows 10 is surely in UEFI mode but the typical configuration of most manufacturers in UEFI is "UEFI+CSM" - allowing for both UEFI and Legacy modes - and this tend to confuse users and led them inadvertently to boot in Legacy/BIOS mode sometimes).
Once confirmed - live session - the computer is working as it should then go ahead, replace the drive, boot the Ubuntu USB stick and use the default settings to install. It should work fine but if not, like after installing it doesn't boot / complains about the boot device, etc., a word of advice: Do nothing! Come back here and post a new specific question. Do not be tempted to follow some random advice from the internetz because more often than not well meaning advice from many pages is outdated, not applicable or completely wrong.
