Slow speeds in Windows 8 may be due to the poisoned DNS cache that may contain invalid or expired DNS records. In case the DNS cache gets poisoned, technically known as 'DNS spoofing,' or the IP address of the web server changes, users may face difficulties opening the websites, or sometimes may also get HTTP error messages. In such cases, users are required to clear the DNS cache by flushing the invalid or expired DNS entries. After flushing the DNS cache, the new IP address of the website is then automatically resolved by the DNS client, aka DNS resolver, with the help of its authoritative DNS server. Users should also delete the temporary files stored in the %Temp% folder, which also helps expedite the Internet speed in Windows 8.

How to Flush DNS Cache to Increase Internet Speed in Windows 8
To delete the DNS cache to increase Internet connection in Windows 8 computers, step-by-step instructions given below must be followed:

Log on to Windows 8 computer with the account that has the elevated privileges.
Click Desktop tile from the Start screen to go to the desktop window.
Once on the desktop screen, hover the mouse to the bottom right corner of the window.
From the displayed options, click Search.
On the opened Search pane in the right, ensure that Apps category.
On the same pane, type CMD in Apps field.
From the displayed results on Apps window, right-click Command Prompt.
From the displayed advanced options at the bottom of the window, click Run as administrator.
On the displayed User Account Control box, click Yes to provide the administrator approval to open the command prompt with the elevated privileges.
On command prompt window, type IPCONFIG/FLUSHDNS command and press Enter to delete the DNS Cache.
Close the command prompt window when done.

How to Delete Temporary Files from Temp Folder

Log on to Windows 8 computer with the account that has the elevated privileges.
Click Desktop tile from the Start screen to go to the desktop window.
Once on the desktop screen, press Windows + R keys simultaneously to initiate the Run command box.
On the Run command box, type %TEMP% in the available field and press Enter.
On the opened Temp window, press CTRL + A keys simultaneously to select all the files.
Once selected, press Delete to remove all the temporary files.
Close Temp window when done.