I tried to install Ubuntu 18.04.1 LTS on my laptop Acer TravelMate p248-mg, using a USB-Bootable. I selected my USBBootable from the boot manager to load the bootable, then installed it. After installation, Ubuntu says it is complete, and I must restart my laptop. After I restart, why does it always load the MS-windows-10? I am expecting it to first show the GRUB, but it always loads to MS-windows-10.