Remove the crank arms using a wrench to remove the spindle nut and pull the crank. If the crank arms are stuck to the spindle bearings, use a crank puller on the plastic dirt cap threads.
Grease the tip of a cotton bud and use it to transfer the lubricant on the spots where the crank and the spindle are stuck. Because of electrolytic action, corrosion is caused between the spindle and the crank, resulting in them becoming stuck. Grease can help you loosen the parts and remove the crank more easily.
Rock the crank after you have applied the grease. If you see even the tiniest bit of movement, keep applying grease and rocking the cranks until it is detached from the spindle.
Heat the part of the crank touching the spindle with a blowtorch. Heat expands the crank -- especially if it is made of aluminum -- and allows you to pull it off of the spindle with ease.
Hold the crank from its unheated outer parts. Pull the crank gently to remove it from the spindle. It is not necessary to replace either the crank or the spindle, as long as you grease the parts regularly to prevent corrosion caused by electrolytic action.