Be careful of agents and property seminars. What they will tell you is "don't sell your HDB flat. Rent out your HDB flat, then buy condo. Use HDB rental to pay for condo mortgage payment". They tell you all the pretty picture. What they didn't tell you is that the market price and rental are falling. We are going to have a huge oversupply of rental properties, so you may not even get a tenant. Some more, if price drop by 30% and your loan is 80%, then you are in deep problem. The banks may ask you to top up as you are underwater. So if market drop by 30%, both your HDB and condo value drop by 30%!

The best thing to do now is to sell your HDB and get a high price and then buy a condo within your means. Best is to put downpayment of 40%, so if market drop by 30%, you are still above water and bank will not call you. Right time to upgrade to condo if you can afford. Highly risky time to buy investment property.