Quote
A very considerable military reduction is about to take place in this neighbourhood:—Portsea Barracks are to be taken down; no troops will be garrisoned there in future. Hilsea Barracks are to be contracted to hold only 1000 men; they formerly held 1500. Fort Cumberland to be reduced from 700 to 500 men. Great reductions are also to take place at Gosport. Report, however, states, that the Royal Marine Artillery are to have a great increase, and be quartered at Fort Monckton.
— Hampshire Chronicle, Monday 29 July 1816 source
Interesting that it was contracted to hold 1500 men, but in June 1795 they managed to squeeze 3500 prisoners in there. I haven’t found any evidence of upgrades between 1795 and 1816 (yet).