bozhenko Hello
It's defined in language file of footer module:
root/language/en-GB/mod_footer.ini
MOD_FOOTER_LINE1="Copyright © %date% %sitename%. All Rights Reserved." ; Note : %date% will be auto replaced by current year! Don't translate
MOD_FOOTER_LINE2="<a href=\"https://www.joomla.org\">Joomla!</a> is Free Software released under the <a href=\"https://www.gnu.org/licenses/gpl-2.0.html\">GNU General Public License.</a>"
You can override this language constant: MOD_FOOTER_LINE2 in Backend >> Language overrides >> add override for your own language.