How to Change Ramdisk Size without Restarting

ramdiskubuntu-12.04

I have the following line on my fstab file:

ramdisk /tmp tmpfs mode=1777,size=2048m

Now I want to increase the size to 4096m.

What I did is change it to:

ramdisk /tmp tmpfs mode=1777,size=4096m

and issue the command:

mount -a

but when I check it if it change using df -h, the value is still the same at 2gb.

Anyone know how to change it?

Typing mount -o remount,size=4096m /tmp should do the trick.