S5-95U additonal 4Kb memory

Dear Sir / Madam,

I have 2 CPU 6ES5095-8MC01 same model and version.

I online and check with Step 5 saw  one CPU with 20Kb program memory, another CPU with only 16Kb program memory.

Kindly refer to attach picture, 

1st CPU with Program memory 40FF , 16KB

2nd CPU with program memory 50FF, 20KB

Any body can advise how add the additional 4Kb into the CPU with 16Kb memory .

Thank you very much for advise.