You can learn their general moves and then you can devise ways to defeat them more easily. Check your accuracy with the F9 key to show your current status. If you are still struggling, you can restart the game and lower the difficulty level to something easier. If you run out of or are low on ammo , you should look for more as soon as you can. You can use your sword as a close-up weapon, but it is not very effective.
Ammo is located throughout each level, and also look for secret doors and areas to find more.
If your inventory becomes full , you can drop objects. You can drop them on the ground anywhere, no one will touch them. Just remember where they are. You do not have to get rid of every single enemy you encounter. If you are stuck in the game, you can go to a prayer altar and may get help.