What is the difference between 'I almost completed...' and 'I have almost completed...'
I almost completed
Indicates an action in the past, which you were doing, and is all gone now. So you say "I almost completed the running race, but had to stop half-way through."
I have almost completed
Means something is still ongoing, and you expect to finish soon. "I have almost completed the race, there are only 500m to go."
(The tense names give these two away - "almost completed" is past tense, "have almost completed" is present perfect.)