This guide was made 10 years ago on Trueachievements.com by a user called McD76 all credit goes to him as i am not he.

This achievement is unlocked by getting all upgrades on all the weapons, spells, and health and magic bar upgrades. The easiest way to get this with the least grinding is to do the following:

1) Play through the game on Easy difficulty
2) Play through the game on Normal difficulty
3) Play through the game on Hard difficulty
4) Start a new game on Chaos difficulty and play through Level 1, then Retire from the game. Start another new game on Chaos difficulty and grind Level 1 again. You should get 550 upgrade points every time for an S ranking. Repeat until you have enough points to complete all upgrades.

I grinded on hard level 1st and got 350 points. When I needed about 100 left I moved on to Chaos and got 550 points and it took me only 18 minutes. I recommend grinding on Chaos. It's not that hard. Just keep repeating element shot with the normal gun on the demons and they should catch fire and drop pretty fast.

This is the order I did my upgrades but feel free to change depending on your gamestyle:

I focused on a balance on
1) health-magic-element shot-normal gun upgrades at first.
2) spear rose-cannon gun-willpower-ravens panic. (The last one is very handy for using on groups of demons)
3)magic wall-sacrifice-shotgun-gatlin gun (I hardly ever used the last two gun forms)