From all you have said it sounds as though the chain needs sharpening. You will need the correct sized file for this and also need to get the angle right.
As you sound to be a novice user you may find this difficult so, for what it would cost, it may be easier for you to simply buy a new chain.
You will not be able to get too close to the ground so an opion is to trench around the remaining stumps which would enable you to take them off far closer to/at/just below ground level by a series of cuts all around the stumps into the centre. The result will be a bit of a hollow which you can then either light a fire in to burn the rest out or just backfill.
Whatever you do, wear some proper protective gear and be very careful.