myeongsangeul hamyeon seuteureseureul deol su isseoyo.

Because 명상 is being treated as a noun in the pattern noun + (을/를) 하다.

• 명상 = meditation
• 명상을 하다 = to do meditation / to meditate

This is very common in Korean, especially with words that can combine with 하다.

So:

• 명상하다 = to meditate
• 명상을 하다 = to do meditation / to meditate

Both are natural.

하면 comes from 하다 + -면, the conditional ending meaning if or when.

So 명상을 하면 means:

• if you meditate
• when you meditate

In sentences like this, it often has a general meaning: if/when one meditates, this result happens.

Yes, but the difference is small.

• 명상하면 comes from the verb 명상하다
• 명상을 하면 uses the noun 명상 plus 하다

Both mean essentially the same thing: if/when you meditate.

A rough nuance:

• 명상하면 sounds a bit more compact
• 명상을 하면 can feel slightly more explicit, because it shows the noun 명상 as the thing being done

In everyday speech, both are natural.

Korean uses:

• -을 after a noun ending in a consonant
• -를 after a noun ending in a vowel

So here:

• 명상 ends in ㅇ (a consonant sound) → 명상을
• 스트레스 ends in 스 (a vowel sound) → 스트레스를

They are the same particle, just in two forms.

덜 수 있어요 means can lessen, can reduce, or can relieve to some degree.

It is made from:

• 덜다 = to lessen, reduce
• -(으)ㄹ 수 있다 = can / be able to

So 스트레스를 덜 수 있어요 means:

• you can reduce stress
• it can help relieve stress

The important nuance is that 덜다 usually means make less, not necessarily remove completely.

It is:

• 덜다 → verb stem 덜-
• -(으)ㄹ 수 있다 → ability/possibility pattern
• polite ending -어요

So:

• 덜다
• 덜 수 있다
• 덜 수 있어요

This grammar pattern is very common:

• 먹을 수 있어요 = can eat
• 볼 수 있어요 = can see/watch
• 할 수 있어요 = can do

Since 덜다 ends in ㄹ, it becomes 덜 수 있다, not 덜을 수 있다.

Because Korean often leaves out the subject when it is obvious or general.

So this sentence could imply:

• you can reduce stress if you meditate
• people can reduce stress if they meditate
• one can reduce stress through meditation

Korean does this very naturally. The subject is understood from context.

있어요 is the standard polite style, often called 해요체.

It is:

• polite
• natural in everyday conversation
• not stiff or overly formal

Compare:

• 덜 수 있어요 = polite everyday
• 덜 수 있어 = casual
• 덜 수 있습니다 = formal

So the original sentence is polite and neutral.

It is closer to can reduce stress.

The object 스트레스 is something being lessened:

• 스트레스를 덜다 = lessen/reduce stress

If you wanted to focus more on feeling less stressed, Korean might use different wording, such as expressions involving:

• 스트레스가 줄다 = stress decreases
• 마음이 편해지다 = your mind feels more at ease

So the original sentence focuses on the amount of stress becoming less.

Usually it sounds like a general truth or general advice.

Because of -면:

• 명상을 하면 스트레스를 덜 수 있어요 = If/When you meditate, you can reduce stress

This sounds like something generally true or commonly possible, not just one specific occasion.

If you wanted a more specific one-time situation, the context would usually make that clear.

Yes. Some common alternatives are:

• 명상하면 스트레스를 덜 수 있어요.
  Same meaning, slightly more compact.

• 명상을 하면 스트레스가 줄어요.
  If you meditate, stress decreases.

• 명상을 하면 스트레스를 줄일 수 있어요.
  If you meditate, you can reduce stress.

These are all natural. The original sentence is perfectly fine and easy to understand.