Cut half position on oanda

Newbie question, sorry if it's silly

I am testing oanda. my question is:
Imagine i am in a trade and i sell 2 full lots. the market moves +25 pips in my direction and i wanna close 1 lot and let the other running. In metatrader platform we have a option to close half the size of our position, but i can't find any option on oanda to do that...
What can i do? Any help is appreciated.
BEst regards!

if youve bought 1000 units eurusd, then just sell 500 units eurusd.

I fairly certain but test with a small amount, or on demo first please. dont blam me

Zunk is correct, using Oanda simply sell/buy 1/2 the position if your intention is to close 1/2.

OK, i will try that! Thank you both..