Legends are really quite different in ArcGIS Pro. I've spent a lot of time digging around in the settings to figure it out. You can still enable/disable each label/heading/etc option for each layer by clicking on the layer in the Legend list, and then viewing the Legend properties.
Format each bit of text by selecting it from the drop down list at the top.
Clicking on the Legend header in the table of contents will show you the overall Legend Properties in the Elements Pane and the drop down list will have more options for you to customise.
I hope that helps.