This will take you into the UEFI/BIOS screen.
Some of the steps are from memory, so if something doesn't work please let me know. I believe I have an answer that allows you to install Ubuntu 14.04.2 alongside Windows 8.1 on an Acer Aspire ES1-512. After several unsuccessful attempts to install Ubuntu alongside Windows.
As it happens this course requires the students to use Ubuntu.
Recently, I bought an Acer Aspire ES1-512 for a college course.