The hard reset or factory reset of the Sony Xperia SL is much the same as the Sony Xperia TX LT29i as well as the Sony Xperia C2305 and the Sony Xperia T2 mobile phone. You will note that the reset process is the same as the other mobile phones in the Xperia range from Sony. You can find more of this on this website including the mobile specs and user manuals of the mobile phones.
You can reset the phone by code, menu, button sequence as well as via the Xperia companion software which you can download from this website. Note that you are best advised to backup all your data before you do a reset of the phone. You cannot recover the settings or the data once the phone has been reset.
Hard Reset will erase all of your data
All described operations you are doing at your own risk.
Hard Reset Sony Xperia SL
Hard Reset Sony Xperia SL with the Menu
Hard Reset Sony Xperia SL by Code