To change your staking user level, first go to the Staking Program page. It is accessed by clicking on the account name in the upper right hand corner of the page and selecting Staking Program from the drop down menu.
You will be presented with 4 level options:
By clicking on the appropriate lock button you will open a dialog box that will ask you for the wallet from which the tokens should be locked as well as confirmation that you understand that the locking period is processed and begins at 00:00 UTC every day. If you are using 2FA, a security code will also be necessary.
It is possible while locking your tokens to exchange them for PLS tokens and take advantage of the Loyalty Rewards Program as well. Please note that at this time PLS tokens are not available in the US.
Once you click the "Lock" button you will receive a confirmation message. Your request will process at 00:00 UTC and your tokens will be locked for 1 month, during which time you will receive the reduced trading fees of the appropriate level.