version problem

i am new to wordpress, i installed it for learning and getting know-how of its working at my localhost/machine. i downloaded version 2.6.1 but when i logged on as an admin then it ws displaying version 2.3.1 at bottom of page and recommanding to upgrade. today i downloaded latest 2.6.2 but still it is displaying that old 2.3.1 version, ma i know that what could be the reason behind this problem?