Where do I find and change user interface displays?
Any fields that are showing on a front-facing contribution or event page would be managed through the configuration of each contribution or event page (or the price sets or profiles associated with them) - to find the configuration area of a given contribution or event page:


Contributions > Manage Contribution Pages > Scroll to find the contribution page of interest, then click on the "Configure" hyperlink and select the area you wish to configure
Events > Manage Events > Scroll to find the event page of interest, then click on the "Configure" hyperlink and select the area you wish to configure


If you are referring to a back office registration (e.g. Event > Register Event Participant), then custom code would be required to change the data entry form.

Hope this helps,
Tamar