I want to make the MTU bigger. What should I do?

Two DA14580 devices are master slave relationships,I want to change MTU to 53 or 153, should I use gattm_set_max_mtu() to change before the connection and negotiate after the connection is successfully?

I used them to try, but after sending the data, the device suddenly got stuck:

gattm_set_max_mtu(53);
tu = gattm_get_max_mtu();

gattc_set_mtu(connection_idx,tu);
get_mtu = gattc_get_mtu (connection_idx);
app_prf_enable(param->conhdl);