For many reasons, you might require a deodexed, zipaligned and debloated ROM for your Samsung galaxy core. The ROM is plain stock, and does not have any bloatware, and is deodexed, and zipaligned. To install, follow these steps. Just make sure to backup your data before proceeding.
1. Download the ROM from here and power off your phone.
2. Boot into CWM recovery by pressing home+power+volume up
3. Select wipe data / factory reset
4. Select wipe cache
5. Flash the zip
6. Do steps 3-4 again.