Hi,
you can delete older transnational log backups which are in /<HANA_Installation>/HDB<instance>/backup/log/"
use some command like "find . -mindepth 1 -mtime +15 -delete" inside that directory.
this will free up the space . /<HANA_Installation>/HDB<instance>/backup/log/"
also check the data size "/<HANA_Installation>/HDB<instance>/backup/data/" , If this is main contributer increase the size.
Thanks,
Razal