How can I find the optimize value of 'C' or ' Boxconstraint' for linear SVM ?

I work with linear svm. but it not gives better output as I required.But when I change BoxConstraint it gives good output. now i want to do something so that i can find optimize value for "Boxconstraint".

tem = templateSVM('kernelFunction','linear','Solver','SMO','BoxConstraint', 16); 
classifier = fitcecoc(trainingFeatures,trainingLabels,'Learners',tem);