If it can be done at all (not all drives permit disabling of the feature), it can be done from the "Recorder"->"Choose Recorder" dialog box. Select your recorder, then press the "Options>>" button in the lower left corner. If the feature can be disabled, it will show up as a check-box. Uncheck it and you are done.
Do consider that there may be a reason it is burning your 48x CD-R at 32x. You might want to try a different brand of media. Check TheWizard's media compatibility thread for ideas: