The solution is quite simple, you can either add the path of the GLPK solver (gpsol.exe) to you user environment variables or / and you can specify the path to the solver directly on your script. Something like this:
path_to_glpk = r'C:\GLPK\glpk-4.65\w64\glpsol.exe'
solver = pulp.GLPK_CMD(path=path_to_glpk)
model.solve(solver)