Here is a list of the options provided:

IdReference NameFasta URLIndex URLSupplementary Tracks
chm13v2.0Human (T2T CHM13-v2.0)chm13v2.0.fachm13v2.0.fa.faiCAT/Liftoff Genes, Augustus, Genes
chm13v1.1Human (T2T CHM13-v1.1)GCA_009914755.3_CHM13_T2T_v1.1_genomic.fnaGCA_009914755.3_CHM13_T2T_v1.1_genomic.fna.faiAnnotations, Genes
hg38Human (GRCh38/hg38)hg38.fahg38.fa.faiRefseq Genes
hg38_1kgHuman (hg38 1kg/GATK)GRCh38_full_analysis_set_plus_decoy_hla.faGRCh38_full_analysis_set_plus_decoy_hla.fa.faiRefseq Genes
hg19Human (GRCh37/hg19)hg19.fastahg19.fasta.faiRefseq Genes
hg18Human (hg18)hg18.fastahg18.fasta.faiRefseq Genes
mm39Mouse (GRCm39/mm39)mm39.famm39.fa.faiRefseq Genes
mm10Mouse (GRCm38/mm10)mm10.famm10.fa.faiRefseq Genes
mm9Mouse (NCBI37/mm9)mm9.fastamm9.fasta.faiRefseq Genes, Genes
rn7Rat (rn7)rn7.farn7.fa.faiGenes, Genes
rn6Rat (RGCS 6.0/rn6)rn6.farn6.fa.faiRefseq Genes, Genes
gorGor6Gorilla (Kamilah_GGO_v0/gorGor6)gorGor6.fagorGor6.fa.faiRefseq Genes, Genes
gorGor4Gorilla (gorGor4.1/gorGor4)gorGor4.fagorGor4.fa.faiRefseq Genes
panTro6Chimp (panTro6) (panTro6)panTro6.fapanTro6.fa.faiRefseq Genes, Genes
panTro5Chimp (panTro5) (panTro5)panTro5.fapanTro5.fa.faiRefseq Genes, Genes
panTro4Chimp (SAC 2.1.4/panTro4)panTro4.fapanTro4.fa.faiRefseq Genes, Genes
macFas5Macaca fascicularis (macFas5)macFas5.famacFas5.fa.faiGenes, Genes
GCA_011100615.1Macaca fascicularis 6.0 (GCA_011100615.1)Macaca_fascicularis.Macaca_fascicularis_6.0.dna.toplevel.fa.gzMacaca_fascicularis.Macaca_fascicularis_6.0.dna.toplevel.fa.gz.faiAnnotations, Genes
panPan2Bonobo (MPI-EVA panpan1.1/panPan2)panPan2.fapanPan2.fa.faiRefseq Genes, Genes
canFam3Dog (Broad CanFam3.1/canFam3)canFam3.facanFam3.fa.faiRefseq Genes, Genes
canFam4Dog (UU_Cfam_GSD_1.0/canFam4)canFam4.facanFam4.fa.faiGenes
canFam5Dog (canFam5)canFam5.facanFam5.fa.faiGenes, Genes
bosTau9Cow (ARS-UCD1.2/bosTau9)bosTau9.fabosTau9.fa.faiRefseq Genes, Genes
bosTau8Cow (UMD_3.1.1/bosTau8)bosTau8.fabosTau8.fa.faiRefseq Genes, Genes
susScr11Pig (SGSC Sscrofa11.1/susScr11)susScr11.fasusScr11.fa.faiRefseq Genes, Genes
galGal6Chicken (galGal6)galGal6.fagalGal6.fa.faiNCBI Refseq Genes
GCF_016699485.2Gallus gallus (GCF_016699485.2)GCF_016699485.2.faGCF_016699485.2.fa.faiGenes, RefSeq Transcripts
danRer11Zebrafish (GRCZ11/danRer11)danRer11.fadanRer11.fa.faiRefseq Genes, Genes
danRer10Zebrafish (GRCZ10/danRer10)danRer10.fadanRer10.fa.faiRefseq Genes, Genes
ce11C. elegans (ce11)ce11.face11.fa.faiRefseq Genes
dm6D. melanogaster (dm6)dm6.fadm6.fa.faiRefseq Genes
dm3D. melanogaster (dm3)dm3.fadm3.fa.faiUCSC Refseq Genes
dmel_r5.9D. melanogaster (dmel_r5.9)dmel-all-chromosome-r5.9.fastadmel-all-chromosome-r5.9.fasta.faiTranscripts
sacCer3S. cerevisiae (sacCer3)sacCer3.fasacCer3.fa.faiRefseq Genes
ASM294v2S. pombe (ASM294v2)Schizosaccharomyces_pombe_all_chromosomes.faSchizosaccharomyces_pombe_all_chromosomes.fa.faiPombase forward strand, Pombase reverse strand
ASM985889v3Sars-CoV-2 (ASM985889v3)GCF_009858895.2_ASM985889v3_genomic.fnaGCF_009858895.2_ASM985889v3_genomic.fna.faiAnnotations
tair10A. thaliana (TAIR 10)TAIR10_chr_all.fasTAIR10_chr_all.fas.faiGenes
GCA_003086295.2Peanut (GCA_003086295.2)GCF_003086295.2_arahy.Tifrunner.gnm1.KYV3_genomic.fnaGCF_003086295.2_arahy.Tifrunner.gnm1.KYV3_genomic.fna.faiAnnotations
GCF_001433935.1O. sativa IRGSP-1.0 (GCF_001433935.1)GCF_001433935.1_IRGSP-1.0_genomic.fna.gzGCF_001433935.1_IRGSP-1.0_genomic.fna.gz.faiMSU V7 genes
NC_016856.1Salmonella enterica subsp. enterica serovar Typhimurium str. 14028SNC_016856.1.fnaNC_016856.1.fna.faiNC_016856.1.gff.gz
GCA_000182895.1Coprinopsis cinerea okayama7#130 (GCA_000182895.1)GCA_000182895.1.faGCA_000182895.1.fa.faiGene models

More info about these options can be found here.

To update the reference genome within the viewer, navigate to the top toolbar and click on the editing icon represented by a pen, which is located adjacent to the current genome name display.