I install dynare first, then I installed econometrics toolbox of LeSage, the “irf” function of dynare is overridden by econometrics toolbox’s. How can I switch back and forth to use any of them if I want to? I tried to install dynare again, but “irf” of econometrics toolbox was overridden by dynare’s again. Aren’t there any way to make them no conflicts? 
If you go to File -> Set Path you can make sure the Dynare paths are above the Econometrics Toolbox Paths when using Dynare and vice versa.