Please help :(

[Chrisp88]

so i have a jail broken iPhone 4 and planning to sell it to get an iPhone 4s but i try to restore it and it don't let me i try to update it to ios5 and says 'the select build is not eligible' so i don't know whats wrong when i jail broke it i did it with redsnow tethered ..the iPhone is verizon 4.2.10 .. can someone please help me to restore it back to factory setting ...