The verb that you are looking for is "to improve."
"to improvise," means to do something without planning.
To improve means to become better or to make something better as in:
"They have improved our seats."=the seats are better now.
"I want to improve in speaking English"= I want to make my English better.
Improving=getting better, making better
Improvising =is the act of going along with a strategy you have made up on the spot without prior planing.
"I have not studied for the test so I'll just improvise"
"Tom forgot his lines, but being the resourceful little genius he was he decided to improvise."