How do you downgrade from 4.2.10 back to 4.8.10?

[metzy25]

Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_2_8 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8E401 Safari/6533.18.5)

I have a iPhone 4 and was looking into how too do this? Is it possible? And how do I do it?

 

[jonrando]

There is no iOS 4.8.10.

If you meant 4.2.10, then you can't unless you saved your SHSH blobs because Apple stopped signing previous versions of iOS.