How to delete a space and the string after space, in a entire column ?

Helo, could you help me with the next issue?

I need delete a first space and the string after their space, in a entire column

Example with just a row:

select pointname
from from_ap
where pointname like 'AER_4L_SA6____I%';

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say:

AER_4L_SA6____I Corriente Sal.06 33kV

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I want:

AER_4L_SA6____I

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It is possible to do using SUBSTR, INSTR or regular expressions, in every column 'pointname'?

Thank in advanced!