Should I change a home to cash out some cash since the unit is fully paid? I was told Singapore home should not stay too long more than 15 or 20 years?

If you have property agent friend, maybe seek their advice?

You'll have to consider not only the monetary costs to purchasing a new unit but also the effort to take to find a new unit, the paperwork required, the renovation coordination, moving and packing which is something both mentally and physically exhausting, might not be everybody's cup of tea.

Lol. Property as investment is not for everyone so I suggest you check your financial means before you play with property investment.

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But of course, if you know what you are trying to achieve, like upsizing or downsizing for logical reason or poor property quality, then go ahead.

If you don't mind moving then why not?