we got a T610 with perc H200 and 1x150GB and 1x300GB (<-this was build in cause the old one had an error, both SAS 15k) in Raid 1
My plan is to change the old 150gb to an another 300gb and let build up the array after this.
but how to use the free space after this? Could i delete the virtual disk and build up new with all data? without loosing my data and without reinstalling?
no, the way you plan to rebuild is not a valid way. You may loose all the data.
When you delete the RAID and create a new one it will destroy all data on it. You may try creating another 150GB RAID on the same drives and use this as additional space.
But the best solution is creating a backup of the actual system - delete the RAID - create a new one and copy the backup back.