MetaTrader 4 allows you to close only a portion of your open position rather than the entire trade. Here's how to perform a partial close:
Locate your open trade in the Terminal window (at the bottom of your MT4 platform)
Right-click on the trade you want to partially close
Select Close Order from the position's context menu to open its Order window. You can also open this window by double-clicking the position.
Check the execution mode shown for that symbol. If it requires a quote request, use Request to obtain a current quote before closing; do not assume every symbol uses Market Execution.
In the Volume field, enter the amount you wish to close (not the amount you wish to keep)
Check the position and entered volume, then use the Close button, not Buy or Sell. Check the execution result, remaining volume in Trade, and Account History.
Example: If you have a 1.0 lot position of EUR/AUD and want to close 0.03 lots, enter 0.03 in the Volume field. After execution, your remaining position will be 0.97 lots, which you can verify in the Trade tab of the Terminal window.
Close By Trades in MetaTrader 4
The "Close By" feature allows you to close opposite positions of the same symbol against each other:
Open the Terminal window (Ctrl+T)
Go to the Trade tab
Double-click one of the opposite open positions to open its Order window.
In the Order window, select Close By in the Type field, rather than looking for it only in the context menu.
In the dialog box that appears, select the opposite position (e.g., a sell position)
Click "Close" to offset the positions against each other
If the positions have different volumes, the smaller position will be closed completely, and the larger one will be partially closed, with the remaining volume still open.
These are MT4 desktop instructions. The example is illustrative: both the volume closed and the volume left open must satisfy the symbol's applicable volume rules. Close By availability depends on the account and symbol. If the option is unavailable, do not assume it is supported. Review the result and Account History; sending a request does not guarantee its execution or price.