Girls heavy lifting

Hey all. Need some help. I do mostly cardio and some weights
And know I need to change it up. I need that last stone off but bodies
On a Plato. I want to start lifting properly as i know this is a good next step.
But not sure how heavy I should be going and how many reps etc and should I do free
Or what?? Help! I know everyone's different but roughly do I do a small amount
Of as hard as possible and 3 sets or do I do a set amount a start building up weights etc.
I know there is some really good advice on here so hoping to tap into it
Thank you!!!! Xx