Google play store .apk not signed properly

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http://forum.xda-developers.com – I was trying to upload apk of MY theme at google play store But play store gives error "Google Play does not accept apks signed with the debug certificate. Create a new certificate that is valid for at least 50 years." what to do now how to sign apk valid for play store Sent from my GT-I9100 using xda app-developers app (HowTos)