Today Microsoft has finally released Windows 8.1 Preview version for its users, you can download and install it for free of cost. This new version comes with lots of changes and enhancements one of them is that it allows you to disable Hot Corners, earlier there were some apps which allows you to do but in Windows 8.1 you dont need any apps and it can be do within pc.
To disable Hot Corners you can do is :-
Right-click on Taskbar and select Properties option.
Now you will see Taskbar and Navigation properties window.
Click on “Navigation” tab and uncheck following both options present in “Corner navigation” section
When I point to the upper-right corner, show the charms
When I click the upper-left corner, switch between my recent apps
Apply the changes and and you are done, it will immediately disable your hot corners