Step 1.
Head over to the main account you want to move the other account data to.
Mouse over the cogwheel up in the right corner of the acccount and select "merge".
Step 2.
Search for the account you want to transfer data from. The searched account will be "deleted" after the merge, all the data will be found on the account you merged the data to.
Step 3.
The amount of data which were found and will be merged to the existing company is displayed. All correct?
Hit Merge!