CRAM is a compressed version of the BAM/SAM formats.
To convert a CRAM file to BAM, you can use the SCRAMBLE conversion tool.
% /software/sciops/pkg/staden_io_bin/1.14.9/bin/scramble -I cram -O bam 27541_1#9.cram > 27541_1#9.bam
where /software/sciops/pkg/staden_io_bin/1.14.9/bin/scramble is where SCRAMBLE is installed,
27541_1#9.cram is the input CRAM file,
27541_1#9.bam is the output BAM file.