I've got a pair of black Corcoran tanker boots. They're great boots in my opinion, but with one problem: the "insole" is glued very firmly to whatever part of the boot is below the insole. Sorry, I don't know what its called, the midsole maybe? Point being that the crappy foam like insole is glued quite firmly to the inside of the boots and I need a way to remove it, as it's degrading in the heel area after only about 8 or 9 months of wear and I want to put an aftermarket insole in the boots. 

I tried just putting an aftermarket insole in on top of the glued in insoles, but it makes the fit too tight in the toe-box/vamp area, so it has to come out. I recognize that the insole in the boots will be destroyed by removing it and thats fine, its garbage anyway. I just need to get it out. I thought about using heat to soften the glue then scraping the insoles out, but I don't want to fuck up the leather and I don't know if that would even work. I have no experience/knowledge with stuff like this, so I need some help. Let me know if you need more info, I'm sure I left something important out. 

So, what say GD? How do I get these damn insoles out?

It entirely depends on the particular construction of that boot.

"Back in the day" when boots were made by hand, the construction was very similar,
but now, with modern plastics, injection moulding, etc. things are very different between mfgrs.

I suggest just mechanical removal, tear it out piece by piece, with pliers etc.
A LITTLE concentrated heat may help, but not too much, as you say, dont want to shrink the toe box any more.

Have you tried contacting the mfgr ? They may have techniques to do what you need. Warranty?

Good Luck !!!!

I tried contacting Corcoran and that got nowhere fast, didn't even reply to my emails. Guess I could try calling them, but I'm unimpressed by their customer service thus far. 

Assuming the insoles are the same as the Corcoran Field Boots, I've done this many times.  Granted it's been almost 10 years since I've worn Corcorans.  But that insole was glued in there like a mofo, but I just kept pulling on it, starting from heel to toe and eventually it comes out.  The insole actually stays together fairly well.  

I'm not sure why they do it that way, it's a bad system when you want to replace the insole, which isn't anything special.  The boots last much longer than that poor insole.

Alright, so I'm sitting here trying to rip this stuff out and it is a BITCH.  

It is not coming out whole, I can only get out small chunks and it often leaves a layer where the glue soaked into the foam more. It can be scraped off, but its not easy. Anyone else got any ideas?

Whatever idiot at Corcoran thought fucking perma-gluing their sub-par insole in was a good idea needs a beating and a pink slip. 

OP is there a shoe repair place near you?  If so, take the boots there and ask if they can do anything.  

You might also try warming up the insoles using a hair dryer or heat gun.  That might soften up the adhesive on the insoles enough to remove them, but if you use too much heat it might also damage your boots.

I hate glued in insoles.

Just googled and it seems there is. May just have to take them there if I get too frustrated with it myself. Like I said, I thought about trying heat (I do have a heat gun with a fairly wide adjustment range...) but I don't know how hot I can get the boots without doing damage. 

Seriously though, why the hell would you glue in insoles?  This is the one and only pair of boots/shoes I've had like that.

Couldn't tell you.  I have a pair of Chippewa 25290s that are great boots except for the god damned glued-in insole made of cheap foam.