In some cases in my work the solution is did not converge untel I changed the value of under relaxation factors My question is is changing of the value of URF affect the results i.e the accuracy of solution

thank you

No, it will not affect solution accuracy as long as your solution converges (with certain mointor indications: residuals, force, surface...).

is that is mean when I choice any value for these factors it will never affecting the results and solution accuracy just enhance the convergance.?

usually we use to set the URF at a low value that what generally it is suggested everytime , but it does effect the solution more over whenever your solution conveges it dosen't mean that the analysis u run is correct always cross verify ur results with contours , graphs and compare the theorotical value and and the values which were calculated from fluent.

only then you can say that ur proposed analysis is correct.