To upgrade a separate power supply?

Thanks to @hilde45  hilde45 I know to just replace them. Thanks also to Paul McGowan of PS Audio for informative clips.

@hilde45 . Thanks. Very helpful.

Look here

and here.

Or, how many years since it was last turned on? If it's in frequent use and working correctly, it may not need replacement electrolytic capacitors. 

After how many years should the caps be replaced.?

On the other hand my Brown Electronics Lab BEL 1001 died after a few weeks use! Needs new power supply caps. It too was built in the mid-80's.

My 40 year old Sumo Andromeda amp has been in daily use for six years with no issues! Designed by the great James Bongiorno of GAS Ampzilla/Dynaco 400/SST fame.

Depends on the voltage rating of the caps, what voltage is applied to the caps, and the ambient air temperature surrounding the caps.