Hi, is it possible do downgrade from windows 8 to windows 7 ?

I don't know what model you have but I can't see why not. I have been successful in upgrading (yes I do mean upgrading) Windows 8 to Windows 7 on my M5-581TG. I doubt you will find any 'downgrade rights' that apply to general consumers thought. Bear in mind that Windows 7 costs considerably more that Windows 8. I would suggest you simply bin Windows 8, purchase Windows 7 version to suit and go from there. Also bear in mind that Acer won't give you any assistance whatsoever if you change the OS from that originally supplied with your laptop. Having said all that, only do it if you have a reasonable understanding and knowledge as it is not simply a case of loading the new OS.

A few pointers/notes:

Make sure you clear *All* BIOS passwords before you do anything!

Check your partitions and fully understand the consequences of modifying your HDD prior to making any changes. (You may currently have four partitions.)

You may wish to make a backup in case you ever wish to revert to Windows 8.

Look into UEFI vs. Legacy as they use different formats (GUID/NTFS). (I changed BIOS to legacy.)

I suggest *NOT* changing BIOS (Win8 BIOS is fine for Win7 at least on my M5).

In my case I needed to run Win8 version of Acer nVidia drivers (due to BIOS nVidia string?).

If you do go ahead, check your Event Viewer for any errors and correct if/as necessary. (You may need to edit your registry if you have Intel errors for example.)

Check your device drivers and ensure you have loaded everything and they are working ok.

Consider modifying nVidia drivers direct from their site (assuming your Acer uses them) so you are not dependant on Acer to supply them (they seem to be slow to update). (I am currently on 314.22)

Finally, do not proceed because I suggest it may be possible - If you do attempt it, you do so entirely at your risk. If you break it you get to keep all the pieces!!!!