Suggestions or Advice Please?

[De Van Do]

hello everyone!

Currently we have a second house that we use as a rental, purchased 6 years ago for $365K, we currently owe $240K and comps for similar size house for sale are in the area range around $550K in San Diego (where the rental is located).  We are considering purchasing our first apartment complex and would like to know what's the best way to tap into our rental for cash to use as a downpayment for our future apartment unit (looking for 5-10 unit in San Diego).  

We would love to keep this rental as this was our first home 6 years ago, but to have the amount need for a downpayment for our apartment complex, we think our only option is to sell our rental since we have some equity in it?  

Any suggestion/advice you can give would be greatly appreciated, thank you Forum users!

Mr. DvD