Can I upgrade to SRAM GX Eagle from Shimano Acera 9 Speed?
To clarify things, with a SRAM GX Eagle groupset that consits of a crankset, GXP bottom bracket, chain, gear shifter, cassette and rear derailleur the only part that might cause incompatibility issues is the cassette because the XG-1275 11-50 cassette requires an XD freehub driver body (XD body has extra space for 10 and 9 cogs, while Shimano-style body does not).

Still, you've got several options to choose from:


Get a more expensive XG-1295 or XG-1299 11-50 cassette (Shimano freehub body compatible).
Get a cheaper Sunrace CSMZ90 11-50 casstte  (Shimano freehub body compatible).
If your rear hub has compatible XD freehub body for sale, get it and a regular XG-1275 10-50 cassette.
If there's no XD freehub body available for your rear hub, you can buy an XD rear hub and relace the rear wheel. Or buy a complete, compatible wheel.