To update a currently configured mailbox in outlook you will need to do the following:
Step 1: Select "File" as shown in the screenshot below.
Step 2: Select "Account Settings" as shown below.
Step 3: Within the list of accounts select the account you wish to modify (Make sure when selected the account shows highlighted) and then select "Change"
Step 4: Once the "Change Account" setting page appears you can now update the Incoming and Outgoing Mail server settings as shown below:
Step 5: To save your settings and confirm they are correct click "Next" to complete a Mail Server test as shown below:
Step 6: Select "Close" to complete the setup. Your account settings have now been updated successfully.