Incorrect spelling, explanation: phrases that are made from two or more words usually can’t be written together as one word. As well is such phrase, so we have to write these two words separately. Thus aswell is incorrect. Words in a phrase can have different meaning by themselves and together. As well is the way we should write down this phrase.

Correct spelling, explanation: This form is correct as as well contains of two words. It is a phrase that is made from a preposition and an adverb. We cannot write this phrase as one word, therefore aswell is an incorrect spelling and the only correct one is as well.

Definition of as well:
phrase, besides, too, the same way as something else
Is Jenny going to be there as well?
This isn’t a big deal; you might have as well told me earlier.