boot your vm with a linux livecd like Ubuntu Mate or something. once booted use gparted to shrink your / partition and grow /boot to 1G . This will work given the fact that your / has some space left.
Or there is another way. From VMware documentation here :
For Workstation 7 and later and Player 3.x and later, you can increase the virtual disk from the GUI:
Select the virtual machine from the Inventory.
Click Edit Virtual Machine Settings.
Click Hard Disk.
Click Utilities > Expand, enter the new size, then click Expand.
Complete the steps in Increasing the size of a disk partition (1004071), so that the guest operating system is aware of the change in disk size.
add 1G using above steps. using Gparted move your partitions around and resize /boot .