Hi Beatriz,
The index of an element is determined by the number of elements that come before: the first element has index 0 (since 0 elements come before), the second element has index 1, etc. However, this is a dynamic number: if you remove an element before another element, all elements after the one removed have now an index that's one lower than before, as one less element comes before it (it's deleted).
Of course, you could compensate for this, e.g. by subtracting the CurrentRowNumber of the second list from the index in the Current of that list (this works because every time you delete an element, all further elements are decreased by one more, so if you're about to remove the third element, the CurrentRowNumber is 2, so if, say, the original index was 11 than it's now at 9 since two elements are deleted).
However, I'd advise you to do it differently: instead of removing elements, you could add the elements that you want to keep to a second list, so that you create a new list with all elements to be kept. When done, you can then assign that list to the original list. Of course, this is only a good strategy if the list you have is fairly small, and/or the size of each element is fairly small, and/or the number of items to keep isn't that large. If you have a very large list, with large elements (e.g. various Entity records) and you need only remove a couple of items, what I proposed above is probably better.