is it possible to do this from outside?

the window that i need to replace is over the cistern (yeah i have an old house...) and getting to the window from inside will be kind of a pain in my ass. but i noticed today that there is a gap between the window and the foundation that is probably an inch or so high and another 5 or 6 wide... :ugh: need to fix that to keep critters out of my basement, not to mention the draft that it creates.

if i can do it from outside, that would make life a whole lot easier.