Microsoft labelled Windows 8.1 as an upgrade for tax purposes, but it is not an upgrade. Windows 8.1, by itself, is a complete operating system that is similar to Windows 8. When you installed it, you lost your Acer drivers and voided your warranty. However, it isn't hopeless.
Go to Computer (formerly "My Computer") and see if your original recovery partition is still there. If it is there, you might be able to restore Windows 8.
But hold on. The manufacturer might come out with drivers later on. Does your laptop have WiFi? Is 8.1 working all right everywhere else? Acer might come out with drivers later on as well. If you can still use WiFi without problems, you might be better off considering it a fair trade--you gave up your Bluetooth for a newer operating system