A triangle has sides whose lengths are 5, 12, and 13. A similar triangle could have sides with lengths of
(1) 3, 4, and 5 (3) 7, 24, and 25
(2) 6, 8, and 10 (4) 10, 24, and 26
A similar triangle would have sides that are in proportion to your original one, that is, the ratio of each of the 3 sides and each of the original 3 sides should all be equal. For example, a triangle with sides 3, 4, 5 and a triangle with sides 6, 8, 10 are similar triangles since: $\displaystyle \frac{6}{3} = \frac{8}{4} = \frac{10}{5}$.
Which of your triangles fit the description?