This is very simple, there is an attribute for this (you need to look for documentations to see everything that exists in each element) although it is recommended not to use it anymore. I'm going to use an example that uses the attribute to follow the style you're using, but your HTML is well out of the one you use today. tags as <center>
should not be used too, the use of <iframe>
that should also be avoided seems to be being abused too. Another problem is that something tells me that you are using tag to compose layout when it was just made to create tables as the name itself says.
<table border=0>
<table>
documentation.
Note that the same can be obtained more appropriately with CSS:
#tabela {
border: 0px;
margin: 0px auto;
width: 500px;
height: 600px;
}
<table id="tabela">
<tr>
<td>
texto1
</td>
</tr>
<tr>
<td>
texto2
</td>
</tr>
</table>