Use System.IO.Compression.FileSystem.dll which exist in C:\Windows\Microsoft.NET\assembly\GAC_MSIL\System.IO.Compression.FileSystem\v4.0_4.0.0.0__b77a5c561934e089
Namespace Name :- using System.IO.Compression.FileSystem
Use below code in class file :- ZipFile.ExtractToDirectory(strZipfilePath, strDestinationPath);
strZipfilePath :- Compressed folder path
strDestinationPath :- Uncompressed file path