If you scale the image in Photoshop it is likely that all of the georeferencing data and scaling will be lost. For GeoTiff data you should use QGIS or some other GIS software that will know what to do with that data and scale it accordingly without losing the tags.
You want to look for the 'Translate' feature and set the 'outsize' to whatever percentage you want.
Here is the sample command that should be shown:
gdal_translate -outsize 25% 25% filename.tif