$ iconv --from-code=ISO-8859-1 --to-code=UTF-8 latin1.txt > utf8.txt
or simply
$ iconv -f ISO-8859-1 -t UTF-8 latin1.txt > utf8.txt
$ iconv -t ISO-8859-1 -f UTF-8 inputfile > outputfile
$ iconv --from-code=ISO-8859-1 --to-code=UTF-8 latin1.txt > utf8.txt
or simply
$ iconv -f ISO-8859-1 -t UTF-8 latin1.txt > utf8.txt
$ iconv -t ISO-8859-1 -f UTF-8 inputfile > outputfile