It is not advisable to directly upgrade a production installation without testing in a stage area first.
To do this, you need your current installation copied to the stage machine. You do this by copying your to the stage machine in the correct place.
Then, install the new version that you want to test (using the production download which you obtain by using the URL and credentials emailed to you when you purchased). Do not try to use a trial installer - it won't work.
Once you have performed your tests to your satisfaction, you can on the production machine.
Note that because the stage machine will have an invalid license, it will only accept connections from localhost, so if you are testing client interactions you will need to do them on the stage machine.