How do you say "officer is downgraded" or "lowered" in status?

In the corps (Police, army, ...) there are grades that go from Private, lieutenant, ... general.

What do you say when some officer rank is lowered in status?

Say that he is a General and for bad behaviour he is taken back to be a Private.

How do you say when some officer get's his rank lowered the status?.

Say that he is a General and for bad behaviour his is taken back to be a Private

The noun would be "demotion", the verb "demote".

https://en.oxforddictionaries.com/definition/demote

In the British army the phrase is reduced to the ranks.

The following is the OED entry on the very term:

b. orig. Mil. to reduce to (formerly also †into) the ranks: to demote (a non-commissioned officer) to the rank of private; (more generally) to strip (any officer or official) of his or her seniority; to demote. Also in extended use.>

?1758 C. W. Direct. Execution Militia Act 9 To serjeants to be reduced into the ranks, which is the purport of this clause.

1768 Gen. Wolfe's Instr. Young Officers 58 The lieutenant-colonel is determined to reduce to the ranks all such as are wilfully negligent, or too ignorant for their stations.

1800 Caledonian Mercury (Electronic text) 20 Dec. Before this took place, the Emperor [sc. the Czar of Russia] met him, and in consequence, he was reduced to the ranks, and his servant made an officer in his place.

1844 Queen's Regulations & Orders Army 149 Non-commissioned Officers may be reduced to the Ranks by the Sentence of a Regimental or other Court-Martial.

1869 T. W. Higginson Malbone ii. 69 The girls complained that in private theatricals no combination of disguises could reduce Kate to the ranks, nor give her the ‘make-up’ of a waiting-maid.

1908 S. M. Crothers By Christmas Fire v. 208 He rebukes even the Captains of Industry, and when they answer insolently, he suggests that they be reduced to the ranks.

1967 S. Mackay Old Crow vi. 31 She had once deprived a vicar of his living and, as a girl, had a captain reduced to the ranks.

1993 S. McAughtry Touch & Go vii. 54 Instead of being reduced to the ranks and put on shithouse fatigues, he was transferred to Air-Sea Rescue on Walrus amphibians.