This is a more interesting question than you realise Patricio.

If you are talking about tidying up the bed after sleeping in it, the correct way to say it is 'make the bed.' This is the standard way to express this which will never be wrong, and which everyone will understand.

e.g.

Have you made your bed yet?

I have to make my bed in the morning before going to school.

So you would say 'I make my bed every day.'

I don't want to confuse the issue but for completeness sake there are situations where we might use 'to do the beds' in informal speech, at least in British English. We sometimes talk about doing the bed(s) as part of housework, or a general task or chore. For example:

I'll start on the vegetables as soon as I've done the beds.

I just have to do the bed and then we can go out.

We can go to the shops as soon as I've done the beds.

'Do' here just refers to a general task that you need to complete. This usage applies to other things as well. For example, you might hear someone say something like 'I just have to do the rubbish' which means 'I just have to take the rubbish out.' This is informal, idiomatic language.

The correct answer is "make the bed."

Paul's right. I didn't want to complicate the issue, just know that the general, all-purpose phrase is "to make the bed."

If you've bought a self-assembly bed and it's not yet assembled, then "making the bed" would mean "building the bed." Once the bed's built, "to make the bed" can only mean one thing i.e making it look neat and tidy.

Thank you very much Suzana, that was very kind of you. Paul threw a lot of light to my doubt, but your help is welcome too and very appreciated.