That's far from huge. Anyway, determine which rows need to be deleted and then set those rows to null. For example if the undesireable rows are where the first column has negative numbers then do this
rowsToBeDeleted = data(:, 1) < 0;
data(rowsToBeDeleted, :) = []; % Set to null to remove the entire row.
Or, equivalently you could do
goodRows = data(:, 1) > 0;
data = data(goodRows, :); % Extract only the good rows.
Please invest 2 hours in the basics and it will save you time:
