Doing so will have unpredictable effects on your game. Either unzip (extract) directly or move the package file to your Mods\ Packages folder within (OS Win:) Documents\ Electronic Arts\ The Sims 3 directory and overwrite any older copy of the mod you have installed.Note: By default, Windows will open zip files just like file folders, displaying the contents directly in the explorer window. In Windows, this can be performed by right-clicking on the file and using the Open With. Find the file on your HDD and unzip (extract) the content from the file.Note: With your Internet Browser you're able to open the zip file directly and extract the content on your HDD by doing so you can skip step 4. At the bottom of the mod's download page will be a download link for the zip file containing the mod.See Patch Level Compatibility for details. Next, click on the appropriate Phase for your Patch-Level.Locate the mod's download page, by clicking on the appropriate mod link on the left-hand side.
