Shortening Matrix to specific number

I have a matrix 139776 x 1. I need to shorten the matrix to 138240 x 1.

How can I do this?

Also, Is there a way to shorten the matrix to the nearest factor of Y.

Thanks

[Walter Roberson]

Do you want to just discard the extra values, or do you want interpolation ?

[sam van Bohemen]

discarad them

Answer 1

[Walter Roberson]

YourMatrix(138240+1:end) = [];

[sam van Bohemen]

thanks for your help