I don't know what you are trying to do, since there isn't a guide that I know of on this site that uses that WAD Manger. The one we recommend to be used is Wii Mod 3.2.
One block is 128k (8 blocks per meg). So 220 blocks is 27.5 megs, which is more than reasonable, depending on what it is (most N64 games are larger than that, for comparison).
If the WAD results in a channel installed, you can go into Wii Settings -> Data Management -> Channels and from there delete the channel or move the channel to SD card to free up space. Moving to SD card makes it launchable from SD Card Menu by copying back a temp copy to system memory to launch it from, so you would want to be sure to have about 250 block free after you are done with everything to make room for this temp copy, if you choose to do it this way.
If the WAD is one that doesn't result in a channel, you need the WAD again to uninstall it from memory using the WAD MAnager. Careful which type of WAD it is though, if it's something like Dios Mios which replaces the stock Mios and you delete it, you have no Mios and that can cause damage, so the way to "uninstall" Dios Mios is to reinstall the stock Mios on top of DM, still taking up some space, but I think less than DM.