WHSmith has moved from its two-storey location within the shopping centre to a single unit on the opposite side of the mall.
The new unit, on the ground floor, was left vacant when Poundworld closed in July last year and is now open to shoppers.
It was also recently revealed that River Island, which has a store in Abington Street is set to move inside the shopping centre.
Grosvenor Centre manager James Roberts said he was always looking at ways to grow and improve the shopping experience.
Although the deals do not bring new high street names to the town, Mr Roberts said they were a vote of long-term confidence from current brands
He said: "There are still positive news stories around retail here. There are still retailers willing to invest and be here.
"WHSmith is staying with us. They're renegotiated their lease and are moving into a newly-fitted store.
"And we've got River Island coming to us, over two floors.
"This is showing commitment to the centre and the town that they are remaining, that there's a market here for retailers.
"This is positive encouragement of people investing in the town."
It is not yet known whether River Island will take over all of the former WHSmith store.
River Island has been approached for comment about its decision to leave Abington Street.