To convert Amber extract, you need to know what malts were used to create the extract, along with the amounts (percentage-wise) of each malt.
Briess makes available the malts used (Two-Row, Munich and Crystal 60), but they don't say how much of each is used. The pilsen malt as is adequately subs for two-row, so you only have to worry about the Munich and Crystal. Munich malt needs to be mashed, so you'll need to do a partial mash.
Long story short, it'll be easier to buy amber extract and use the pilsen extract for something else.