At this time, the IDA Search does not have the option to select individuals that have progressed in diagnosis. This is a feature that we hope to add in the future, but it is not yet available. If you want to identify individuals that progressed from MCI to Dementia, the easiest strategy would be to download the ADNIMERGE.csv file ("Key ADNI tables merged into one table" under the Study Info section on the Study Data page) and use the diagnosis information at each visit.