How do i study japanese to get to N3 as quick as possible

Guys, Im confused.

I have a strong n5 base with kanjis is strong but prolly shaky vocab and grammar. Similarly for n4 i have shaky kanji base, with shaky grammar and shaky vocab.
I want to get to n3 as quick as possible, how do i do it? I just need sources for kanji vocab and grammar which are all free and i can follow them to get good at japanese. Pls help