It depends. What format is it now? Easeus may allow you to change partition sizes without destroying the data (if it's not WBFS) but I've never tried it. Though it is best to fully back up the data, format it clean the way you want it, then restore the data.
Though, our recommendation (at least mine) is to do a single FAT32 partition of the entire hard drive. We have a guide for that that shows you how to install your games greater than 4 gigs to it without it failing (link in signature).