The phrase "top up to" is correct and usable in written English.
It is used to say that something is being increased to a larger amount. For example: "I topped up my phone credit to $25."
Add the apple juice and the honey and thyme syrup and top up to just below the rim with ice.
Pour the beer into a measuring jug and top up to the 400ml mark with some syrup from the cherries.
* Ping Pong, a London chain of dim sum restaurants, confirmed, after a tip-off to The Independent, that it uses service charges to top up to or above the minimum wage.
Stir through the sugar. 2 Put the egg yolk and creme fraiche in a measuring jug, then top up to the 170ml level with milk and tip the lot into the bowl with the flour and mix well.
"Arsenal and Tottenham both offered me the chance to come over and work with their academies while I studied for a foundation degree in coaching but I didn't want to do that because I didn't want to then have to go elsewhere to top up to a full degree and lose time.
It used to have a virtual currency-centric model where players would have to top up to continue playing in multi-player mode.
