6 days a week training

For your goals, a full body workout is perfect. Follow a proven program for best results, don't create your own.. and don't target your fatty areas extra. Can't spot reduce fat. What strength equipment do you have available?

If by "loose" arms you mean you have some extra fat on your arm, you won't be able to target just that fat by working your arms. Your body will lose fat where it wants to assuming you are eating in a caloric deficit. If you're not eating at deficit levels, you can work your arms all you want, but you'll keep the fat and just build muscle underneath. So to tighten up your arms, I think diet should be your first focus. After that, full body workouts (however you decide to split it up) will add muscle everywhere which with a good diet will "tighten" everything up.

If you're a beginner, which I assume you are based on the question, common best practice is to do full body workouts. Once you've been lifting for a while, then you could branch out and split your workout up by bodypart. For example I've been lifting a number of years and do a 4-day+1 split -

Day 1 - Chest/triceps
Day 2 - Back/biceps
Day 3 - Shoulders
Day 4 - Legs
Day 5 - Upper Body