mkdir ~/download
cd ~download
# then download the tgz, then untar
tar zxvf <tgz_file>
#[Option 1: if ~/download/.opera contains chaindata folder only]
# remove ~/.opera/chaindata if it exists
mv ~/download/chaindata ~/.opera
#[Option 2: if ~/download/.opera contains chaindata and other subfolders]
#remove ~/.opera if it exists, make sure you backup the keystore folder.
# then move the untarred .opera into a path
mv ~/download/.opera ~/.opera
You can also download md5 checksum file <tgz_file>.md5.