I seems to me, that you play to quickly. You missed some quite obvious moves just because you moved without thinking/looking for best moves. Maybe try some longer time controls. Some tactical training (puzzles) may also help.
Then your opening play can be better. Try to focus on getting these three things done first: influence in centre, develop all your pieces, getting your King in safety.
The best way to converting is to be strong in endgames. So learning basic endgames will be a good idea.
These are 2 recent games, it is very typical stuff for me, I get to a +5 advantage 20-30 moves in but then have great difficulty converting this into a win. In fact I end up winning both games only by timeout. I have of course gone through the analysis, but I'm more interested in the general strategy that I'm missing?
https://www.chess.com/analysis/game/live/140589460186/review
https://www.chess.com/analysis/game/live/140589938998/review