Current delivered from op-amp output to load depends on voltage at the output, load resistance Rl, output resistance Ro and your series resistance Rs. Current through load can be determined from Ohm's law. In that case Io=Uo/(Rs+Ro+Rl). Considering that Ro is internal resistance of opamp which is integrated circuit, you cannot chamge it. So the only wau to increase current is to lower the load resistance or the series resistance. You must take into consideration that the output current causes power dissipation in internal resistance, which can be determined from the formula P=I^2*Ro. You musn't exceed your opamp's maximum power dissipation or you are risking damage to it.