How can I modify the size of label in boxplot?

I created a boxplot with by the following function:

h= boxplot([tas_O2,tas_DeQM,tas_KeQM,tas_Dv,tas_Kv],'labels',{'Obs','M1_e','M2_e','M1_v','M2_v'});

I would like to change the original size of the labels. Could someone write me what I should to do?