1. Download and install the USB drivers for I9300
Download Odin v3.09 and run
2. Turn off your phone and Put phone in download mode (volume down+home+power)
3. Download ok twrp file from twrp support From Here .
4. Select twrp in AP/PDA And then flash
5. After flash go to recovery mode (volume up+home+power)
6. Download latest aroma file manager from Here.
7. Copy in SD card and go to install from twrp recovery.
8. After install go to(data>system> Gesture key) must be deletes.
9.And exit then reboot phone Done 100%. Thanks
For more details, please watch following video:
S3 I9300 Remove screen lock witout loss data using TWRP recovery witout any box