Here's an easy way to upgrade your tablet Asus Memo FHD 10 (ME303C) to Android 4.3 if your have the US SKU.
Download the firmware WW from Asus support site.
Unrar the file using an unrar app. There a ton of them available for free.
Rename your zip file from WW to US. Use the File Manager by clicking the arrow at the right of the file.
Copy the renamed zip file...
Paste the zip file into the root of your device (/sdcard).
Press an hold the power button for a complete shutdown and restart.
Once rebooted, your tablet will notify you that there is an update available.
Proceed with the update. It should take around 10 minutes to complete.