Correct spelling, explanation: the main rule of forming adverbs in English is by adding an -l ending to an adjective. Thus, following this rule when you add an -l to personal (an adjective), you will get the correct form, which is personally. You need to double the last letter -l of an adjective.

Definition of personally:
1. adverb – used to show your opinion or to state that you do something on your own.
Personally, I think you should quit this nasty habit of smoking.
Unfortunately, I haven’t read the book personally, but I read some good reviews of it.

Collocations with personally:
The most common collocation is to take something personally, which refers to a remark that somebody may find offensive,
Don’t take it personally, but I think you should reconsider your behavior.

Incorrect spelling, explanation: both native speakers of English, as well as learners, often find it confusing how to form an adverb from an adjective when it already ends in an -l letter. The problem of course refers to the fact of whether to double the -l letter or not. The answer is that in most cases we need to double it. Therefore, the correct form is personally and not personaly.