Unable to increast rootfs size

[alarm@alarmpi ~]$ lsblk                                                                                                                                                                                                                     NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT                                                                                                                                                                                              mmcblk0     179:0    0 29.8G  0 disk                                                                                                                                                                                                         ├─mmcblk0p1 179:1    0  100M  0 part /boot                                                                                                                                                                                                   └─mmcblk0p2 179:2    0   24G  0 part /                                                                                                                                                                                                       [alarm@alarmpi ~]$ df / -h                                                                                                                                                                                                                   Filesystem      Size  Used Avail Use% Mounted on                                                                                                                                                                                             /dev/mmcblk0p2  1.9G  1.5G  300M  84% /

Basically, before it even had its first boot, I increased partition2 size. but while it is able to detect it is larger, it does not utilize it.

does anyone know how to fix this? SO that i can use the extra storage?