Once you have collected data, Graphical Analysis doesn’t allow you to change the Data Collection Mode or Time Units. The reason for this is that those types of changes break the X axis: different data sets then have different meanings for the X axis, which makes plotting them against each other problematic.

If those options are grayed out, Choose the “File” icon in the upper left corner, and then choose “New Experiment.” (It will ask you if you want to save your existing data.)