OK, the info is there in the links posted.
http://www.kb2ljj.com/Manuals/22-cb-radios/HR-2510%20Mods.pdf
Look at Step Number 10 in the section about increasing the power output of the Hr2510
With out any real test equipment about all you can do is look for VR 104 that controls the ALC ( Automatic Level Control for SSB ) and Adjust it for Max output while modulating the radio While saying auuuudddddiiiiooooooo into the mic, crude, but that is about all you can do with out a tone generator
that and a good power mic is about all you are going to get.
Really, if you want any more than that requires some surgery, and in the long run, you would be better off putting a small amp behind the radio and not messing with it.
The 2510/2600/Lincoln radios are good rigs, you can not get them anymore, the ones you do find for sale now have often been butchered, and it is really best to leave them alone and just run them the way they are.
This might not be what you wanted to hear, but that is about it.
It is a good radio, take care of it and it will serve you well.
73
Jeff