Click the Apple menu
Select System Settings
Go to General
Click Software Update
Wait for the Mac to check for updates
Click Update Now if an update is available
Enter your administrator password if prompted
Keep the MacBook plugged into power
Wait for the update to download and install
Restart the MacBook if prompted
If you mean a browser refresh, press Command + R
If you mean a Finder refresh, close and reopen the window
If you mean a full system reset, back up your data first