You will find conversion files in the Gene FTP DATA directory. Use the gene2refseq.gz file if all of your accessions are RefSeq accessions. Otherwise, use the gene2accession.gz file. You will be able to get the Gene IDs and the default (official) symbols for the genes. If you are also interested in gene name synonyms, you will need to use the gene_info.gz file subsequently.

All of the files in the DATA directory are described in the README file.