Is heavy weights really necessary for a good butt?

So, all I have access to is very, very light dumbbells and beginners ankle weights. Gym membership is super expensive for me and I don't have spare cash to buy any new equipment. My arse is already quite well shaped, but I'd like to "lift" it a bit. Many youtube videos require the user to use super heavy weights at the gym.. Is there a way to still have a rocking butt without heavy weights? If so, how often in a week and how do I make use of my resources effectively? Currently. I work out 5 times a week. 3 days are HIIT, 2 days running. 2 days are legs and butt, 2 days abs and 1 day arms.

And! My arms are quite slim but I do have a bit of flabby skin around my armpits.. and it's really annoying. Tips? Thanks x
Is heavy weights really necessary for a good butt?
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