Before making any changes, it's important to back up your existing .htaccess file. This step ensures that you can easily restore the original state if any problems occur. You can find the .htaccess file in the root directory of your Joomla installation. To access and edit this file, you can use an FTP client or the file manager in your hosting control panel.

Look for sections in the .htaccess file related to GZIP compression and comment them out.

## GZIP
## These directives are only enabled if the Apache mod_headers module is enabled.
## This section will check if a .gz file exists and if so will stream it
##     directly or fallback to gzip any asset on the fly
## If your site starts to look strange after enabling this file, and you see
##     ERR_CONTENT_DECODING_FAILED in your browser console network tab,
##     then your server is already gzipping CSS and js files and you don't need this
##     block enabled in your .htaccess
<IfModule mod_headers.c>
	# Serve gzip compressed CSS files if they exist
	# and the client accepts gzip.
	RewriteCond "%{HTTP:Accept-encoding}" "gzip"
	RewriteCond "%{REQUEST_FILENAME}\.gz" -s
	RewriteRule "^(.*)\.css" "$1\.css\.gz" [QSA]

	# Serve gzip compressed JS files if they exist
	# and the client accepts gzip.
	RewriteCond "%{HTTP:Accept-encoding}" "gzip"
	RewriteCond "%{REQUEST_FILENAME}\.gz" -s
	RewriteRule "^(.*)\.js" "$1\.js\.gz" [QSA]

	# Serve correct content types, and prevent mod_deflate double gzip.
	RewriteRule "\.css\.gz$" "-" [T=text/css,E=no-gzip:1]
	RewriteRule "\.js\.gz$" "-" [T=text/javascript,E=no-gzip:1]

	<FilesMatch "(\.js\.gz|\.css\.gz)$">
		# Serve correct encoding type.
		Header set Content-Encoding gzip

		# Force proxies to cache gzipped &
		# non-gzipped css/js files separately.
		Header append Vary Accept-Encoding
	</FilesMatch>
</IfModule>