How to increase the rated output voltage/current by connecting multiple op amps?
Stop and think about this.

First, 50 W is way more than anything called a "opamp" is going to provide.  You didn't provide a link to the datasheet, so I don't know what your opamp can do, but it would probably require paralleling many many of them to get 50 W, even if that would work.

Second, to push 50 W into 50 &Omega; requires 50 V and 1 A.  That's again beyond ordinary "opamp" range.

Follow the opamp with some kind of power amp.  You don't say what the frequency range is or whether the output must swing both ways or not, so there is little more to add here.  If your frequencies are in the audio range, for example, then a off the shelf audio power amp would be the easiest solution.