Class 5 huh? What are your grades? If they are A+ You should read the following Mathematics books -
1.Targeting Mathematics for class - 5 by Madhubun (easy)
2.Composite Mathematics for class -5 by R.S. Aggarwal and Vikas Aggarwal (moderate)
3. Advantage Mathematics for class 5 by Lakshmanan/Vasudevan/Rameswari (oxford)
These books will help to improve your grades a lot!