The provided value for soft and hard limit of block must be in bytes.
8388608/1024 =8192/1024 = 8GB
10485760/1024 = 10240/1024 = 10GB
Accordingly, use "edquota" then run the command with "-u" argument as shown below
# edquota -u username
Disk quotas for user username (uid 1005):
  Filesystem                   blocks       soft       hard     inodes     soft     hard
  /dev/mapper/system-tmp            0   8388608   10485760          0        0        0
This will show you the currently set quota limits for the user "username". Here you can make you modification, after which save and exit the file using "wq!"