Hi aizafaraz787,
Here is the link to grade 4 math
https://www.khanacademy.org/math/cc-fourth-grade-math

A quick question do you see a square button in the right corner on your main learning dashboard?

Under math by grade you can select any grade you want to learn from another useful tool is the search box where you can put terms like "Grade 4"  and you will find the content you want to learn from.

i dont see a square button any where what do i do??????!!!!! im trying to go to 7 grade.

same problem I really do not know how to change grade

If you click your username while logged in you will see an option in the drop down menu titled "Learner Home." This will be located in the top right corner. Click this and it should take you to said homepage with all of your courses, streaks, etc. In the corner will be a blue box labeled "Edit Course." By clicking this you will find that not only can you change courses, but that you may also go back (by clicking the word BACK in the bottom left corner of the pop - up) and change your learning level to what suits you at the moment. 

Hopefully this was helpful!