Amping up AK47 Pale Mild recipe?

I just brewed Northern Brewer's AK47 Pale Mild recipe as follows:

SPECIALTY GRAINS

0.5 lbs Simpsons Caramalt

- 1 oz Fawcett Pale Chocolate

FERMENTABLES

- 3 lbs Munton's Light DME (60 min)

- 1 lb corn sugar late addition (0 min)

HOPS

- .75oz Kent Goldings 60 min

-.25oz Kent Goldings 15 min

I was thinking about replacing the Dry Malt Extract and Corn Sugar with just Liquid Malt extract. What would you suggest as a good substitute?

And even though I'm not there yet, how would one convert this to an All-Grain?

They actually have and all grain version of this on their website.Just click on the Details link for the all grain version. You certainly can use liquid but you will have to use a little more to reach the OG.

Takeing out the corn sugar and replaceing it with malt will up the FG a bit so you might want to up your 60min hops addition to balance the extra malt.

Even with their all-grain recipe they still include Corn Sugar

MASH INGREDIENTS
-- 5 lbs. Maris Otter
-- 0.5 lbs Simpsons Caramalt
-- 1 oz Fawcett Pale Chocolate

BOIL ADDITIONS & TIMES
-- 0.5 oz UK Kent Goldings (60 min)
-- 0.25 oz UK Kent Goldings (15 min)
-- 1 lb corn sugar (the end of the boil)

Would one just replace the corn sugar with more Maris Otter? and how much?
Could this sort of thing be figured out with BeerSmith or other similar programs?

I'm actually brewing this today and I'm a little nervous using that much sugar in such a small grain bill. When I put the recipe into beer smith the est og was 1.039 and according to the recipe it should be around 1.035

I don't want to deviate from the recipe, but should I scale back on the sugar a bit?

I wouldn't. I would follow the recipe as stated and then use RO water to top off and get yoru gavity to the reading it should be.