Do you mean it doesn't open or you can't find it ?
To find it, these methods should work.
Click Menu -> Settings
Scroll down the list to 'Software & Updates' and click on it.
OR
Click Menu, then in the search box begin typing the word 'software' - as you type there should be a pop up list in which 'Software & Updates' should appear which you can click on.
If you are clicking 'Software & Updates' and it doesn't open you need explain what happens.