You can try this and see how it goes.
Note: [0] is 0 and [9] is 9. Since we're programmers, we start from 0 instead of 1.
:For(I,1,16
:ClrHome
:DelVar L₁"?→Str1
:For(J,1,I
:randInt(1,10→B
:{102,92,93,94,82,83,84,72,73,74
:Ans(B→L₁(J
:Str1+sub("0123456789",B,1→Str1
:End
:Output(1,1,sub(Ans,2,length(Ans)-1
:rand(10I
:ClrHome
:For(J,1,I
:Repeat Ans
:getKey
:End
:If Ans≠L₁(J:Goto Q
:Output(1,J,sub(Str1,J+1,1
:End
:rand(20
:End
:Lbl Q
:Pause "YOU "+sub("LOSE!WIN! ",1+5(I=17),5
:ClrHome:"
This is probably an assumption, but from the error you are saying, you simply changed the values from 5 to 10, resulting in an INVALID DIM because the code is trying to grab the 10th element from the above list with it only has 5 elements.
So what you had to do, is add in the final five elements the number keys corresponding to their respective codes. The next thing you need to do is update the string. Because of how the game works and how the keypad is, you need to start from 0 and work your way to 9 instead of 1 to 10. You could do 1 to 10, but that requires extra RAM than you really need to use, plus there is no 10 key.