Windows 7:

• Open Start menu
• Click Run
• Type cmd and press enter
• In the Command Prompt type ipconfig /flushdns and press Enter

Windows 8, 10:

• On your keyboard, press Win+X to open the WinX Menu
• Right-click Command Prompt and select Run as Administrator
• Run this command ipconfig /flushdns and press Enter

It is advisable to clear up your browser's cache as well.