Any ways to release RAM after backtest?

Amibroker is lean, fast and usually takes up small RAM space. However, I notice that after a backtest of a large database like U.S stock market, the RAM consumed can be very large. For my PC, it got up to 10Gbyte.

To release RAM, I need to close Amibroker, then launch it again. Are there any ways to release RAM without closing Amibroker?

By the way, even though RAM usage reached up to 95%, Amibroker is still running fast.

The RAM is there to be used, not to be sitting idle. Go to Tools->Performance Monitor to find out what consumes RAM. Most likely it is data cache. It is caching data in RAM for speedy access which is good and desired. You can avoid that if you lower in-memory cache in Tools->Preferences "Data" tab, but then it will work slower as disk access is orders of magnitude slower than RAM.