expand tmpfs on RHEL 7.2

how to expand /tmp mounted on tmpfs in RHEL 7?

Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_root-root 320G 3.2G 317G 1% /
devtmpfs 910M 0 910M 0% /dev
tmpfs 920M 0 920M 0% /dev/shm
tmpfs 920M 8.7M 912M 1% /run
tmpfs 920M 0 920M 0% /sys/fs/cgroup
tmpfs 920M 12K 920M 1% /tmp

I wanted to grow half of root. My root partition hold 320 G. Also I wanted /tmp folder to be part of root instead of tmpfs. How to do that?

I am trying to disable it but still shows up.
[root@k0002414 system]# systemctl mask tmp.mount
Created symlink from /etc/systemd/system/tmp.mount to /dev/null.