Increase RAM for XenServer VM's through Command Line Interface.

If the RAM editing option is grayed out through XenCenter. 

1. Take a putty/ssh connection to pool master
2. Power off the VM.
3. Execute the Below command to configure the new RAM:

#xe vm-memory-limits-set    uuid=<uuid of the valid VM>   static-min=<nn>GiB/MiB  dynamic-min=<nn>GiB/MiB  dynamic-max=<nn>GiB/MiB     static-max=<nn>GiB/MiB

#xe vm-memory-limits-set    vm=<name of the valid VM>   static-min=<nn>GiB/MiB  dynamic-min=<nn>GiB/MiB  dynamic-max=<nn>GiB/MiB     static-max=<nn>GiB/MiB

Example :
#xe vm-memory-limits-set    uuid=120513b6-68ec-c0eb-ba87-b4936bbbc66f      static-min=64GiB   dynamic-min=64GiB   dynamic-max=64GiB    static-max=64GiB
#xe vm-memory-limits-set    vm=linux01      static-min=64GiB   dynamic-min=64GiB   dynamic-max=64GiB    static-max=64GiB

4. Start the VM. 

Problem Cause