First find the wine

WineBase has all sorts of search options that make finding a wine or wines really easy. What search method you use depends very much on the wine you're trying to find.

As a last resort you could just use this button to list every wine in the cellar or the View - Index Listings - All Wines in Cellar menus.
But it's probably better to narrow the search by using one of the more popular search option buttons on the WineBar or failing that the dialog that includes them all.
Search and Sort options dialog...
Which will be listed here

In this rather stumpy Index Listing and as it says on the bottom right hand corner of the window Left click to View or Right click to Edit. The click is a mouse click, left and right is which button on the mouse and you click on the wine itself. You can Right click anywhere along the entry to show the Main Edit dialog (the same one you use to Add a new wine) where you can change any details of that wine and save those changes.

Left click is a slightly different matter because if you Left click on the Vintage a popup menu will appear offering various options, one of which is Edit Wine. Left click on the Age column (the coloured boxes) and you get access to the Tasting Schedule for that wine.

And here's a really useful one if your aim is to just reduce the stock count for a wine by one bottle. Notice how the cursor has turned to a bottle and the hint text, lower left says Quick Drink. Left click here and that's what the program does.

If you Right clicked then you're here...

Where you can change any of the information for this wine and then those changes.

You'll also note that you have full access to the History, Notes and Tasting files and the Duplicate button. The Duplicate button is very handy when you're adding a wine that is very similar to an existing one in your cellar.

For example a later vintage where all you have to do is change the Vintage from say the 2007 as shown here, perhaps adjust the Price and this data as a new wine.