Hello SumodNair
As I understand it you are inquiring as to whether or not Windows 8.1 drivers exist before upgrading to Windows 8.1. I would like to offer you my assistance with this. Now according to the HP ENVY Sleekbook 4-1090se Drivers page there are no drivers for your system running Windows 8.1. I can also confirm that I have been unable to find any Windows 8.1 drivers for your system.
Now keep in mind that Windows 8.1 has built in drivers. This means that even though there does not appear to be any HP drivers for your computer there still may be in the Windows 8.1 update. Personally, I would set a Windows Restore Point and give the update a try. If the update does not work for you simply use the Windows Restore Point to go back to Windows 8. No harm no foul.
I hope this helps answer your question concerning the Windows 8.1 drivers. Thank you for posting your question on the HP Forums. Have a great day!