I´m don´t know what to do, hope you can give me some advices.
I have a Linode with some domains hosted, it´s working, but i think i messed up the server a little, so i want to start a new Linode from scratch to host just one domain.
I want to test the domain in the new Linode before deleting the other account, can i do that? I mean, how can i control which server (IP) is in charge of that domain at that time? By the DNS manager?
Thanks

Yes, you can change the IP address in whatever DNS manager has your site records.

You could also modify the hosts file on your client machine so your test browser thinks the site name is on the second IP, or create a different name in dns (test-www.example.com) though some web/app server config may have to change depending on the construction of your site.

I´m a little confused.
For example: My domain nameserver is pointing to ns1.linode.com.
If i have the same domain in two linodes, how can i control it?
I know that in the A/AAAA Records i give an IP Address in one linode and another one in the other linode.
For testing, if i delete one A/AAAA Records, the other linode will resolve it?
Do you know what i mean?

If you have A records for both servers then clients will go to both servers. Changing the A record from your old to new server will send them exclusively to the new one. Use the Linode DNS Manager to amend the records.

If you're trying to test the server in isolation (keep sending people to the old running for now) then it would be better to change your local hosts file, or use a different site name.