To decompress the archive, use the compressor's corresponding utility.
In the case of a .gz or .tgz file, use gunzip:
gunzip my_archive.tar.gz
or:
gunzip my_archive.tgz
These commands decompress the file, resulting in my_archive.tar. You can also use tar with the -z option to extract from the archive without decompressing it first:
tar -xzf my_archive.tgz